<?xml version="1.0" encoding="US-ASCII"?>
<!--XBRL Document Created with Wdesk from Workiva-->
<!-- -->
<link:linkbase xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <link:roleRef roleURI="http://www.qualys.com/role/CommitmentsAndContingencies" xlink:href="qlys-20161231.xsd#CommitmentsAndContingencies" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/CommitmentsAndContingenciesAdditionalInformationDetails" xlink:href="qlys-20161231.xsd#CommitmentsAndContingenciesAdditionalInformationDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/CommitmentsAndContingenciesFutureMinimumLeasePaymentsDetails" xlink:href="qlys-20161231.xsd#CommitmentsAndContingenciesFutureMinimumLeasePaymentsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/CommitmentsAndContingenciesTables" xlink:href="qlys-20161231.xsd#CommitmentsAndContingenciesTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/CompanyAndSummaryOfSignificantAccountingPolicies" xlink:href="qlys-20161231.xsd#CompanyAndSummaryOfSignificantAccountingPolicies" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/CompanyAndSummaryOfSignificantAccountingPoliciesDetails" xlink:href="qlys-20161231.xsd#CompanyAndSummaryOfSignificantAccountingPoliciesDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/CompanyAndSummaryOfSignificantAccountingPoliciesPolicies" xlink:href="qlys-20161231.xsd#CompanyAndSummaryOfSignificantAccountingPoliciesPolicies" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/ConsolidatedBalanceSheets" xlink:href="qlys-20161231.xsd#ConsolidatedBalanceSheets" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/ConsolidatedBalanceSheetsParenthetical" xlink:href="qlys-20161231.xsd#ConsolidatedBalanceSheetsParenthetical" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/ConsolidatedStatementsOfCashFlows" xlink:href="qlys-20161231.xsd#ConsolidatedStatementsOfCashFlows" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/ConsolidatedStatementsOfComprehensiveIncome" xlink:href="qlys-20161231.xsd#ConsolidatedStatementsOfComprehensiveIncome" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/ConsolidatedStatementsOfOperations" xlink:href="qlys-20161231.xsd#ConsolidatedStatementsOfOperations" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/ConsolidatedStatementsOfStockholdersEquity" xlink:href="qlys-20161231.xsd#ConsolidatedStatementsOfStockholdersEquity" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/DocumentAndEntityInformation" xlink:href="qlys-20161231.xsd#DocumentAndEntityInformation" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/EmployeeStockAndBenefitPlans" xlink:href="qlys-20161231.xsd#EmployeeStockAndBenefitPlans" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/EmployeeStockAndBenefitPlansCommonStockAndPreferredStockDetails" xlink:href="qlys-20161231.xsd#EmployeeStockAndBenefitPlansCommonStockAndPreferredStockDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/EmployeeStockAndBenefitPlansExpenseDetails" xlink:href="qlys-20161231.xsd#EmployeeStockAndBenefitPlansExpenseDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/EmployeeStockAndBenefitPlansFairValueAssumptionsStockOptionsDetails" xlink:href="qlys-20161231.xsd#EmployeeStockAndBenefitPlansFairValueAssumptionsStockOptionsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/EmployeeStockAndBenefitPlansOptionsOutstandingAndVestedDetails" xlink:href="qlys-20161231.xsd#EmployeeStockAndBenefitPlansOptionsOutstandingAndVestedDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/EmployeeStockAndBenefitPlansPlanInformationDetails" xlink:href="qlys-20161231.xsd#EmployeeStockAndBenefitPlansPlanInformationDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/EmployeeStockAndBenefitPlansRestrictedStockDetails" xlink:href="qlys-20161231.xsd#EmployeeStockAndBenefitPlansRestrictedStockDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/EmployeeStockAndBenefitPlansRestrictedStockUnitsAndRestrictedStockAwardsActivityDetails" xlink:href="qlys-20161231.xsd#EmployeeStockAndBenefitPlansRestrictedStockUnitsAndRestrictedStockAwardsActivityDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/EmployeeStockAndBenefitPlansStockOptionActivityDetails" xlink:href="qlys-20161231.xsd#EmployeeStockAndBenefitPlansStockOptionActivityDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/EmployeeStockAndBenefitPlansTables" xlink:href="qlys-20161231.xsd#EmployeeStockAndBenefitPlansTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/FairValueOfFinancialInstruments" xlink:href="qlys-20161231.xsd#FairValueOfFinancialInstruments" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/FairValueOfFinancialInstrumentsCashAndCashEquivalentsAvailableForSaleSecuritiesRestrictedCashReconciliationDetails" xlink:href="qlys-20161231.xsd#FairValueOfFinancialInstrumentsCashAndCashEquivalentsAvailableForSaleSecuritiesRestrictedCashReconciliationDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/FairValueOfFinancialInstrumentsContractualMaturityDetails" xlink:href="qlys-20161231.xsd#FairValueOfFinancialInstrumentsContractualMaturityDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/FairValueOfFinancialInstrumentsFairValueHierarchyDetails" xlink:href="qlys-20161231.xsd#FairValueOfFinancialInstrumentsFairValueHierarchyDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/FairValueOfFinancialInstrumentsNarrativeDetails" xlink:href="qlys-20161231.xsd#FairValueOfFinancialInstrumentsNarrativeDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/FairValueOfFinancialInstrumentsTables" xlink:href="qlys-20161231.xsd#FairValueOfFinancialInstrumentsTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/GoodwillAndIntangibleAssetsNet" xlink:href="qlys-20161231.xsd#GoodwillAndIntangibleAssetsNet" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/GoodwillAndIntangibleAssetsNetDetails" xlink:href="qlys-20161231.xsd#GoodwillAndIntangibleAssetsNetDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/GoodwillAndIntangibleAssetsNetFutureAmortizationDetails" xlink:href="qlys-20161231.xsd#GoodwillAndIntangibleAssetsNetFutureAmortizationDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/GoodwillAndIntangibleAssetsNetTables" xlink:href="qlys-20161231.xsd#GoodwillAndIntangibleAssetsNetTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/IncomeTaxes" xlink:href="qlys-20161231.xsd#IncomeTaxes" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/IncomeTaxesDeferredTaxAssetsAndLiabilitiesDetails" xlink:href="qlys-20161231.xsd#IncomeTaxesDeferredTaxAssetsAndLiabilitiesDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/IncomeTaxesIncomeBeforeProvisionForBenefitFromIncomeTaxesDetails" xlink:href="qlys-20161231.xsd#IncomeTaxesIncomeBeforeProvisionForBenefitFromIncomeTaxesDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/IncomeTaxesNarrativeDetails" xlink:href="qlys-20161231.xsd#IncomeTaxesNarrativeDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/IncomeTaxesProvisionForBenefitFromIncomeTaxesDetails" xlink:href="qlys-20161231.xsd#IncomeTaxesProvisionForBenefitFromIncomeTaxesDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/IncomeTaxesTables" xlink:href="qlys-20161231.xsd#IncomeTaxesTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/IncomeTaxesTaxRateReconciliationDetails" xlink:href="qlys-20161231.xsd#IncomeTaxesTaxRateReconciliationDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/IncomeTaxesUnrecognizedTaxBenefitsDetails" xlink:href="qlys-20161231.xsd#IncomeTaxesUnrecognizedTaxBenefitsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/NetIncomePerShareAttributableToCommonStockholders" xlink:href="qlys-20161231.xsd#NetIncomePerShareAttributableToCommonStockholders" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/NetIncomePerShareAttributableToCommonStockholdersDetails" xlink:href="qlys-20161231.xsd#NetIncomePerShareAttributableToCommonStockholdersDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/NetIncomePerShareAttributableToCommonStockholdersTables" xlink:href="qlys-20161231.xsd#NetIncomePerShareAttributableToCommonStockholdersTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/OtherIncomeExpenseNet" xlink:href="qlys-20161231.xsd#OtherIncomeExpenseNet" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/OtherIncomeExpenseNetDetails" xlink:href="qlys-20161231.xsd#OtherIncomeExpenseNetDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/OtherIncomeExpenseNetTables" xlink:href="qlys-20161231.xsd#OtherIncomeExpenseNetTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/PropertyAndEquipmentNet" xlink:href="qlys-20161231.xsd#PropertyAndEquipmentNet" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/PropertyAndEquipmentNetDetails" xlink:href="qlys-20161231.xsd#PropertyAndEquipmentNetDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/PropertyAndEquipmentNetTables" xlink:href="qlys-20161231.xsd#PropertyAndEquipmentNetTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/QuarterlyFinancialInformationUnaudited" xlink:href="qlys-20161231.xsd#QuarterlyFinancialInformationUnaudited" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/QuarterlyFinancialInformationUnauditedDetails" xlink:href="qlys-20161231.xsd#QuarterlyFinancialInformationUnauditedDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/QuarterlyFinancialInformationUnauditedTables" xlink:href="qlys-20161231.xsd#QuarterlyFinancialInformationUnauditedTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/ScheduleIiScheduleOfValuationAndQualifyingAccounts" xlink:href="qlys-20161231.xsd#ScheduleIiScheduleOfValuationAndQualifyingAccounts" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/ScheduleIiScheduleOfValuationAndQualifyingAccountsDetails" xlink:href="qlys-20161231.xsd#ScheduleIiScheduleOfValuationAndQualifyingAccountsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/SegmentInformationAndInformationAboutGeographicArea" xlink:href="qlys-20161231.xsd#SegmentInformationAndInformationAboutGeographicArea" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/SegmentInformationAndInformationAboutGeographicAreaDetails" xlink:href="qlys-20161231.xsd#SegmentInformationAndInformationAboutGeographicAreaDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.qualys.com/role/SegmentInformationAndInformationAboutGeographicAreaTables" xlink:href="qlys-20161231.xsd#SegmentInformationAndInformationAboutGeographicAreaTables" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension" xlink:type="simple" />
  <link:definitionLink xlink:role="http://www.qualys.com/role/CommitmentsAndContingencies" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.qualys.com/role/CommitmentsAndContingenciesAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_OperatingLeasedAssetsLineItems" xlink:label="loc_us-gaap_OperatingLeasedAssetsLineItems_619AAC0F3B2C97849FDE5E02B19AD976" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ScheduleOfOperatingLeasedAssetsTable" xlink:label="loc_us-gaap_ScheduleOfOperatingLeasedAssetsTable_C260DD83642A1F9C1EB25E02B19790F7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_OperatingLeasedAssetsLineItems_619AAC0F3B2C97849FDE5E02B19AD976" xlink:to="loc_us-gaap_ScheduleOfOperatingLeasedAssetsTable_C260DD83642A1F9C1EB25E02B19790F7" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_LeaseArrangementTypeAxis" xlink:label="loc_us-gaap_LeaseArrangementTypeAxis_A7645E06C29A54D6ED1A5E03594C51CE" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfOperatingLeasedAssetsTable_C260DD83642A1F9C1EB25E02B19790F7" xlink:to="loc_us-gaap_LeaseArrangementTypeAxis_A7645E06C29A54D6ED1A5E03594C51CE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_LeaseArrangementTypeDomain" xlink:label="loc_us-gaap_LeaseArrangementTypeDomain_9816847E4F9C27FBFF5C5E0408749304_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LeaseArrangementTypeAxis_A7645E06C29A54D6ED1A5E03594C51CE" xlink:to="loc_us-gaap_LeaseArrangementTypeDomain_9816847E4F9C27FBFF5C5E0408749304_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_LeaseArrangementTypeDomain" xlink:label="loc_us-gaap_LeaseArrangementTypeDomain_9816847E4F9C27FBFF5C5E0408749304" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LeaseArrangementTypeAxis_A7645E06C29A54D6ED1A5E03594C51CE" xlink:to="loc_us-gaap_LeaseArrangementTypeDomain_9816847E4F9C27FBFF5C5E0408749304" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_LeaseAgreementForHeadquartersMember" xlink:label="loc_qlys_LeaseAgreementForHeadquartersMember_C123000E0A5B35F2951C5E03DCF7FF86" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LeaseArrangementTypeDomain_9816847E4F9C27FBFF5C5E0408749304" xlink:to="loc_qlys_LeaseAgreementForHeadquartersMember_C123000E0A5B35F2951C5E03DCF7FF86" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_CreditFacilityAxis" xlink:label="loc_us-gaap_CreditFacilityAxis_1041D6DDD81B20A80C405E072D9CA476" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfOperatingLeasedAssetsTable_C260DD83642A1F9C1EB25E02B19790F7" xlink:to="loc_us-gaap_CreditFacilityAxis_1041D6DDD81B20A80C405E072D9CA476" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_CreditFacilityDomain" xlink:label="loc_us-gaap_CreditFacilityDomain_53B2A5D4266323F9F3C05E072D9D49B4_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_1041D6DDD81B20A80C405E072D9CA476" xlink:to="loc_us-gaap_CreditFacilityDomain_53B2A5D4266323F9F3C05E072D9D49B4_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_CreditFacilityDomain" xlink:label="loc_us-gaap_CreditFacilityDomain_53B2A5D4266323F9F3C05E072D9D49B4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_1041D6DDD81B20A80C405E072D9CA476" xlink:to="loc_us-gaap_CreditFacilityDomain_53B2A5D4266323F9F3C05E072D9D49B4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_StandbyLettersOfCreditMember" xlink:label="loc_us-gaap_StandbyLettersOfCreditMember_8490CAAD78DC946E67D55E072DB98F49" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_53B2A5D4266323F9F3C05E072D9D49B4" xlink:to="loc_us-gaap_StandbyLettersOfCreditMember_8490CAAD78DC946E67D55E072DB98F49" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_LesseeLeasingArrangementsOperatingLeasesTermOfContract" xlink:label="loc_us-gaap_LesseeLeasingArrangementsOperatingLeasesTermOfContract_1C14CD7DF3F2906EE0285E01C2E108A3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLeasedAssetsLineItems_619AAC0F3B2C97849FDE5E02B19AD976" xlink:to="loc_us-gaap_LesseeLeasingArrangementsOperatingLeasesTermOfContract_1C14CD7DF3F2906EE0285E01C2E108A3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_OperatingLeasesFutureMinimumPaymentsDue" xlink:label="loc_us-gaap_OperatingLeasesFutureMinimumPaymentsDue_546A68E400458371291A5E0527BF31E5" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLeasedAssetsLineItems_619AAC0F3B2C97849FDE5E02B19AD976" xlink:to="loc_us-gaap_OperatingLeasesFutureMinimumPaymentsDue_546A68E400458371291A5E0527BF31E5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_C012331729F378D2D6675E072D89F9E4" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLeasedAssetsLineItems_619AAC0F3B2C97849FDE5E02B19AD976" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_C012331729F378D2D6675E072D89F9E4" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.qualys.com/role/CommitmentsAndContingenciesFutureMinimumLeasePaymentsDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.qualys.com/role/CommitmentsAndContingenciesTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.qualys.com/role/CompanyAndSummaryOfSignificantAccountingPolicies" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.qualys.com/role/CompanyAndSummaryOfSignificantAccountingPoliciesDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_DerivativeLineItems" xlink:label="loc_us-gaap_DerivativeLineItems_D0C42E537139EAC8AC9E5DF615B7418B" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_DerivativeTable" xlink:label="loc_us-gaap_DerivativeTable_2EA06FD95EF7E917C36F5DF615AE1181" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_D0C42E537139EAC8AC9E5DF615B7418B" xlink:to="loc_us-gaap_DerivativeTable_2EA06FD95EF7E917C36F5DF615AE1181" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_StatementScenarioAxis" xlink:label="loc_us-gaap_StatementScenarioAxis_AF79010799AE80B64CA25DFC131E82CA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_2EA06FD95EF7E917C36F5DF615AE1181" xlink:to="loc_us-gaap_StatementScenarioAxis_AF79010799AE80B64CA25DFC131E82CA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ScenarioUnspecifiedDomain" xlink:label="loc_us-gaap_ScenarioUnspecifiedDomain_990E77D9B4BBB1AD85F45DFC1322971D_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementScenarioAxis_AF79010799AE80B64CA25DFC131E82CA" xlink:to="loc_us-gaap_ScenarioUnspecifiedDomain_990E77D9B4BBB1AD85F45DFC1322971D_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ScenarioUnspecifiedDomain" xlink:label="loc_us-gaap_ScenarioUnspecifiedDomain_990E77D9B4BBB1AD85F45DFC1322971D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementScenarioAxis_AF79010799AE80B64CA25DFC131E82CA" xlink:to="loc_us-gaap_ScenarioUnspecifiedDomain_990E77D9B4BBB1AD85F45DFC1322971D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ScenarioForecastMember" xlink:label="loc_us-gaap_ScenarioForecastMember_524304975F1D39B78DF85DFC33559038" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScenarioUnspecifiedDomain_990E77D9B4BBB1AD85F45DFC1322971D" xlink:to="loc_us-gaap_ScenarioForecastMember_524304975F1D39B78DF85DFC33559038" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" xlink:label="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_FA6C060BC32E6F4D93235DFC80977741" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_2EA06FD95EF7E917C36F5DF615AE1181" xlink:to="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_FA6C060BC32E6F4D93235DFC80977741" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_TypeOfAdoptionMember" xlink:label="loc_us-gaap_TypeOfAdoptionMember_D7AE853C7C74A9814B525DFC80A0D318_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_FA6C060BC32E6F4D93235DFC80977741" xlink:to="loc_us-gaap_TypeOfAdoptionMember_D7AE853C7C74A9814B525DFC80A0D318_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_TypeOfAdoptionMember" xlink:label="loc_us-gaap_TypeOfAdoptionMember_D7AE853C7C74A9814B525DFC80A0D318" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_FA6C060BC32E6F4D93235DFC80977741" xlink:to="loc_us-gaap_TypeOfAdoptionMember_D7AE853C7C74A9814B525DFC80A0D318" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_AccountingStandardsUpdate201609Member" xlink:label="loc_qlys_AccountingStandardsUpdate201609Member_5B3C6B2E19BFAFEDFC4F5DFDAD9C7115" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfAdoptionMember_D7AE853C7C74A9814B525DFC80A0D318" xlink:to="loc_qlys_AccountingStandardsUpdate201609Member_5B3C6B2E19BFAFEDFC4F5DFDAD9C7115" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_BBE3055C725D615AE48D5DFE85BD26D3" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_2EA06FD95EF7E917C36F5DF615AE1181" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_BBE3055C725D615AE48D5DFE85BD26D3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_AAFDA6056925D68DA5B35DFE85CBCAF5_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_BBE3055C725D615AE48D5DFE85BD26D3" xlink:to="loc_us-gaap_EquityComponentDomain_AAFDA6056925D68DA5B35DFE85CBCAF5_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_AAFDA6056925D68DA5B35DFE85CBCAF5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_BBE3055C725D615AE48D5DFE85BD26D3" xlink:to="loc_us-gaap_EquityComponentDomain_AAFDA6056925D68DA5B35DFE85CBCAF5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_RetainedEarningsMember" xlink:label="loc_us-gaap_RetainedEarningsMember_CCB9B5F1E675887A031B5DFEC50717C5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_AAFDA6056925D68DA5B35DFE85CBCAF5" xlink:to="loc_us-gaap_RetainedEarningsMember_CCB9B5F1E675887A031B5DFEC50717C5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ConcentrationRiskByTypeAxis" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_21C9DFCB97FFDCE24FDC5DF615AE421A" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_2EA06FD95EF7E917C36F5DF615AE1181" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_21C9DFCB97FFDCE24FDC5DF615AE421A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ConcentrationRiskTypeDomain" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_EC8E9865B336BDB11D445DF615AEAF0A_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_21C9DFCB97FFDCE24FDC5DF615AE421A" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_EC8E9865B336BDB11D445DF615AEAF0A_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ConcentrationRiskTypeDomain" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_EC8E9865B336BDB11D445DF615AEAF0A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_21C9DFCB97FFDCE24FDC5DF615AE421A" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_EC8E9865B336BDB11D445DF615AEAF0A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_CustomerConcentrationRiskMember" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_DEF1A91D20F2FD845B755DF615AE3738" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_EC8E9865B336BDB11D445DF615AEAF0A" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_DEF1A91D20F2FD845B755DF615AE3738" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_17D1A660D3380B5DB5135DF615AFFAEE" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_2EA06FD95EF7E917C36F5DF615AE1181" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_17D1A660D3380B5DB5135DF615AFFAEE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ConcentrationRiskBenchmarkDomain" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_AEF83481EDB11D95C60B5DF615B446BB_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_17D1A660D3380B5DB5135DF615AFFAEE" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_AEF83481EDB11D95C60B5DF615B446BB_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ConcentrationRiskBenchmarkDomain" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_AEF83481EDB11D95C60B5DF615B446BB" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_17D1A660D3380B5DB5135DF615AFFAEE" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_AEF83481EDB11D95C60B5DF615B446BB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AccountsReceivableMember" xlink:label="loc_us-gaap_AccountsReceivableMember_491BC50563CFD3D464285DF615B4C718" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_AEF83481EDB11D95C60B5DF615B446BB" xlink:to="loc_us-gaap_AccountsReceivableMember_491BC50563CFD3D464285DF615B4C718" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_A4EB8AA274FADF278B9E5DF615B5E45B" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_2EA06FD95EF7E917C36F5DF615AE1181" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_A4EB8AA274FADF278B9E5DF615B5E45B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01B711BFA42B0BA1D3475DF615B52843_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_A4EB8AA274FADF278B9E5DF615B5E45B" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01B711BFA42B0BA1D3475DF615B52843_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01B711BFA42B0BA1D3475DF615B52843" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_A4EB8AA274FADF278B9E5DF615B5E45B" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01B711BFA42B0BA1D3475DF615B52843" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_SoftwareAndSoftwareDevelopmentCostsMember" xlink:label="loc_us-gaap_SoftwareAndSoftwareDevelopmentCostsMember_6F8BC7D78F4BA3BC2DD75DF615B5AEF5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01B711BFA42B0BA1D3475DF615B52843" xlink:to="loc_us-gaap_SoftwareAndSoftwareDevelopmentCostsMember_6F8BC7D78F4BA3BC2DD75DF615B5AEF5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_DerivativeByNatureAxis" xlink:label="loc_us-gaap_DerivativeByNatureAxis_42D3A262529FEC0F510C5DF615B5A136" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_2EA06FD95EF7E917C36F5DF615AE1181" xlink:to="loc_us-gaap_DerivativeByNatureAxis_42D3A262529FEC0F510C5DF615B5A136" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_DerivativeNameDomain" xlink:label="loc_us-gaap_DerivativeNameDomain_834A555A7FB949B679E45DF615B53925_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeByNatureAxis_42D3A262529FEC0F510C5DF615B5A136" xlink:to="loc_us-gaap_DerivativeNameDomain_834A555A7FB949B679E45DF615B53925_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_DerivativeNameDomain" xlink:label="loc_us-gaap_DerivativeNameDomain_834A555A7FB949B679E45DF615B53925" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeByNatureAxis_42D3A262529FEC0F510C5DF615B5A136" xlink:to="loc_us-gaap_DerivativeNameDomain_834A555A7FB949B679E45DF615B53925" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ForwardContractsMember" xlink:label="loc_us-gaap_ForwardContractsMember_478D738423D2B45F2B485DF615B5855F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeNameDomain_834A555A7FB949B679E45DF615B53925" xlink:to="loc_us-gaap_ForwardContractsMember_478D738423D2B45F2B485DF615B5855F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_97014C717C94D63ECB565DF615B5FCB1" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_2EA06FD95EF7E917C36F5DF615AE1181" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_97014C717C94D63ECB565DF615B5FCB1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_C2C103DB81B020E24B3E5DF615B6D45A_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_97014C717C94D63ECB565DF615B5FCB1" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_C2C103DB81B020E24B3E5DF615B6D45A_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_C2C103DB81B020E24B3E5DF615B6D45A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_97014C717C94D63ECB565DF615B5FCB1" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_C2C103DB81B020E24B3E5DF615B6D45A" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_ScannerAppliancesMember" xlink:label="loc_qlys_ScannerAppliancesMember_6E926423B2AE537DA6265DF615B62954" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_C2C103DB81B020E24B3E5DF615B6D45A" xlink:to="loc_qlys_ScannerAppliancesMember_6E926423B2AE537DA6265DF615B62954" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_RangeAxis" xlink:label="loc_us-gaap_RangeAxis_E073919DBF0247DEA3BA5DF615B6FDC4" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_2EA06FD95EF7E917C36F5DF615AE1181" xlink:to="loc_us-gaap_RangeAxis_E073919DBF0247DEA3BA5DF615B6FDC4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_B0721BE2A8D329AE95355DF615B660FB_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RangeAxis_E073919DBF0247DEA3BA5DF615B6FDC4" xlink:to="loc_us-gaap_RangeMember_B0721BE2A8D329AE95355DF615B660FB_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_B0721BE2A8D329AE95355DF615B660FB" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RangeAxis_E073919DBF0247DEA3BA5DF615B6FDC4" xlink:to="loc_us-gaap_RangeMember_B0721BE2A8D329AE95355DF615B660FB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_MinimumMember" xlink:label="loc_us-gaap_MinimumMember_BB9922E0BC9D121BE8A35DF615B6F5BF" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_B0721BE2A8D329AE95355DF615B660FB" xlink:to="loc_us-gaap_MinimumMember_BB9922E0BC9D121BE8A35DF615B6F5BF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_MaximumMember" xlink:label="loc_us-gaap_MaximumMember_4AE9990B24BD2721F7715DF615B647AA" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_B0721BE2A8D329AE95355DF615B660FB" xlink:to="loc_us-gaap_MaximumMember_4AE9990B24BD2721F7715DF615B647AA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_NewAccountingPronouncementEarlyAdoptionAxis" xlink:label="loc_us-gaap_NewAccountingPronouncementEarlyAdoptionAxis_57D709A6278C06735D445DF615B6606B" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_2EA06FD95EF7E917C36F5DF615AE1181" xlink:to="loc_us-gaap_NewAccountingPronouncementEarlyAdoptionAxis_57D709A6278C06735D445DF615B6606B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_NewAccountingPrinciplesEarlyAdoptionMember" xlink:label="loc_us-gaap_NewAccountingPrinciplesEarlyAdoptionMember_E3E194BF9299975D99F45DF615B68D0E_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_NewAccountingPronouncementEarlyAdoptionAxis_57D709A6278C06735D445DF615B6606B" xlink:to="loc_us-gaap_NewAccountingPrinciplesEarlyAdoptionMember_E3E194BF9299975D99F45DF615B68D0E_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_NewAccountingPrinciplesEarlyAdoptionMember" xlink:label="loc_us-gaap_NewAccountingPrinciplesEarlyAdoptionMember_E3E194BF9299975D99F45DF615B68D0E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_NewAccountingPronouncementEarlyAdoptionAxis_57D709A6278C06735D445DF615B6606B" xlink:to="loc_us-gaap_NewAccountingPrinciplesEarlyAdoptionMember_E3E194BF9299975D99F45DF615B68D0E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_NewAccountingPronouncementEarlyAdoptionEffectMember" xlink:label="loc_us-gaap_NewAccountingPronouncementEarlyAdoptionEffectMember_DB87EF02667428F776BD5DF615B6BBF7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NewAccountingPrinciplesEarlyAdoptionMember_E3E194BF9299975D99F45DF615B68D0E" xlink:to="loc_us-gaap_NewAccountingPronouncementEarlyAdoptionEffectMember_DB87EF02667428F776BD5DF615B6BBF7" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_ConcentrationOfCreditRiskAbstract" xlink:label="loc_qlys_ConcentrationOfCreditRiskAbstract_B18BE11F1E36A5A2D3435DF615B77930" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_D0C42E537139EAC8AC9E5DF615B7418B" xlink:to="loc_qlys_ConcentrationOfCreditRiskAbstract_B18BE11F1E36A5A2D3435DF615B77930" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_ConcentrationRiskNumberOfCustomers" xlink:label="loc_qlys_ConcentrationRiskNumberOfCustomers_CAC367AD9DB055534FEC5DF615B783FE" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_qlys_ConcentrationOfCreditRiskAbstract_B18BE11F1E36A5A2D3435DF615B77930" xlink:to="loc_qlys_ConcentrationRiskNumberOfCustomers_CAC367AD9DB055534FEC5DF615B783FE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_PropertyPlantAndEquipmentAbstract" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentAbstract_6BBCCA4C6BCF7ED7DC9B5DF615B7979F" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_D0C42E537139EAC8AC9E5DF615B7418B" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentAbstract_6BBCCA4C6BCF7ED7DC9B5DF615B7979F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_PropertyPlantAndEquipmentUsefulLife" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_8849F0FEB94AE2EB6A215DF615B7034C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentAbstract_6BBCCA4C6BCF7ED7DC9B5DF615B7979F" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_8849F0FEB94AE2EB6A215DF615B7034C" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_GoodwillAndIntangibleAssetsNetAbstract" xlink:label="loc_qlys_GoodwillAndIntangibleAssetsNetAbstract_C7CF38D00B7B290BA6EB5DF615B7DBE4" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_D0C42E537139EAC8AC9E5DF615B7418B" xlink:to="loc_qlys_GoodwillAndIntangibleAssetsNetAbstract_C7CF38D00B7B290BA6EB5DF615B7DBE4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ImpairmentOfIntangibleAssetsIndefinitelivedExcludingGoodwill" xlink:label="loc_us-gaap_ImpairmentOfIntangibleAssetsIndefinitelivedExcludingGoodwill_60D83EEA6283E98EDFA45DF615B7FDB8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_qlys_GoodwillAndIntangibleAssetsNetAbstract_C7CF38D00B7B290BA6EB5DF615B7DBE4" xlink:to="loc_us-gaap_ImpairmentOfIntangibleAssetsIndefinitelivedExcludingGoodwill_60D83EEA6283E98EDFA45DF615B7FDB8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ImpairmentOfIntangibleAssetsExcludingGoodwill" xlink:label="loc_us-gaap_ImpairmentOfIntangibleAssetsExcludingGoodwill_4BB6D9CE33B481BE34955DF615B73777" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_qlys_GoodwillAndIntangibleAssetsNetAbstract_C7CF38D00B7B290BA6EB5DF615B7DBE4" xlink:to="loc_us-gaap_ImpairmentOfIntangibleAssetsExcludingGoodwill_4BB6D9CE33B481BE34955DF615B73777" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_2DA1012A2D7A5A035F245DF615B8F552" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_qlys_GoodwillAndIntangibleAssetsNetAbstract_C7CF38D00B7B290BA6EB5DF615B7DBE4" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_2DA1012A2D7A5A035F245DF615B8F552" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ResearchAndDevelopmentAbstract" xlink:label="loc_us-gaap_ResearchAndDevelopmentAbstract_DF647CE63ED2D7C737A55DF615BDBD15" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_D0C42E537139EAC8AC9E5DF615B7418B" xlink:to="loc_us-gaap_ResearchAndDevelopmentAbstract_DF647CE63ED2D7C737A55DF615BDBD15" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_CapitalizedSoftwareDevelopmentCosts" xlink:label="loc_qlys_CapitalizedSoftwareDevelopmentCosts_EA4BB36D33DE308074BB5DF615BDF89F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentAbstract_DF647CE63ED2D7C737A55DF615BDBD15" xlink:to="loc_qlys_CapitalizedSoftwareDevelopmentCosts_EA4BB36D33DE308074BB5DF615BDF89F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsGross" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_CEBDB932D25ABAC2D6435DF615BDFA17" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentAbstract_DF647CE63ED2D7C737A55DF615BDBD15" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_CEBDB932D25ABAC2D6435DF615BDFA17" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_B86245D7532BF81AFB395DF615BD94C3" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ResearchAndDevelopmentAbstract_DF647CE63ED2D7C737A55DF615BDBD15" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_B86245D7532BF81AFB395DF615BD94C3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_SummaryOfDerivativeInstrumentsAbstract" xlink:label="loc_us-gaap_SummaryOfDerivativeInstrumentsAbstract_846CF586A85366C5C8105DF615BDF1D5" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_D0C42E537139EAC8AC9E5DF615B7418B" xlink:to="loc_us-gaap_SummaryOfDerivativeInstrumentsAbstract_846CF586A85366C5C8105DF615BDF1D5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_DerivativeNumberOfInstrumentsHeld" xlink:label="loc_us-gaap_DerivativeNumberOfInstrumentsHeld_A565D8496B55D99DEEE75DF615BEED01" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SummaryOfDerivativeInstrumentsAbstract_846CF586A85366C5C8105DF615BDF1D5" xlink:to="loc_us-gaap_DerivativeNumberOfInstrumentsHeld_A565D8496B55D99DEEE75DF615BEED01" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/invest/2013/invest-2013-01-31.xsd#invest_DerivativeNotionalAmount" xlink:label="loc_invest_DerivativeNotionalAmount_044F71A8DF2C1D07281D5DF615BEB256" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SummaryOfDerivativeInstrumentsAbstract_846CF586A85366C5C8105DF615BDF1D5" xlink:to="loc_invest_DerivativeNotionalAmount_044F71A8DF2C1D07281D5DF615BEB256" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ForeignCurrencyContractAssetFairValueDisclosure" xlink:label="loc_us-gaap_ForeignCurrencyContractAssetFairValueDisclosure_59CBE6B146C134AE4EFA5DF615BEA8DC" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SummaryOfDerivativeInstrumentsAbstract_846CF586A85366C5C8105DF615BDF1D5" xlink:to="loc_us-gaap_ForeignCurrencyContractAssetFairValueDisclosure_59CBE6B146C134AE4EFA5DF615BEA8DC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGain" xlink:label="loc_us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGain_8D1DF34E9807E16BB0B25DF615BE7556" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SummaryOfDerivativeInstrumentsAbstract_846CF586A85366C5C8105DF615BDF1D5" xlink:to="loc_us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGain_8D1DF34E9807E16BB0B25DF615BE7556" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ForeignCurrencyTransactionLossBeforeTax" xlink:label="loc_us-gaap_ForeignCurrencyTransactionLossBeforeTax_5649C6DB94B0E759A0955DF615BE2371" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SummaryOfDerivativeInstrumentsAbstract_846CF586A85366C5C8105DF615BDF1D5" xlink:to="loc_us-gaap_ForeignCurrencyTransactionLossBeforeTax_5649C6DB94B0E759A0955DF615BE2371" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_ForeignCurrencyTransactionGainLossIncludingDerivativesBeforeTax" xlink:label="loc_qlys_ForeignCurrencyTransactionGainLossIncludingDerivativesBeforeTax_C9F8087946571B76BCC95DF617695F0E" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SummaryOfDerivativeInstrumentsAbstract_846CF586A85366C5C8105DF615BDF1D5" xlink:to="loc_qlys_ForeignCurrencyTransactionGainLossIncludingDerivativesBeforeTax_C9F8087946571B76BCC95DF617695F0E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_MarketingAndAdvertisingExpenseAbstract" xlink:label="loc_us-gaap_MarketingAndAdvertisingExpenseAbstract_A8086DFAA91D59B9C0EA5DF615BECCCB" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_D0C42E537139EAC8AC9E5DF615B7418B" xlink:to="loc_us-gaap_MarketingAndAdvertisingExpenseAbstract_A8086DFAA91D59B9C0EA5DF615BECCCB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AdvertisingExpense" xlink:label="loc_us-gaap_AdvertisingExpense_E52B4908A47A2D045E915DF615BE0A74" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketingAndAdvertisingExpenseAbstract_A8086DFAA91D59B9C0EA5DF615BECCCB" xlink:to="loc_us-gaap_AdvertisingExpense_E52B4908A47A2D045E915DF615BE0A74" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ForeignCurrencyTransactionGainLossBeforeTax" xlink:label="loc_us-gaap_ForeignCurrencyTransactionGainLossBeforeTax_FF7CEA4A7D008CC5A5535DF615BE7D65" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_D0C42E537139EAC8AC9E5DF615B7418B" xlink:to="loc_us-gaap_ForeignCurrencyTransactionGainLossBeforeTax_FF7CEA4A7D008CC5A5535DF615BE7D65" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_IncomeTaxDisclosureAbstract" xlink:label="loc_us-gaap_IncomeTaxDisclosureAbstract_0A667AD910A0548399745DF615BF8AE9" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_D0C42E537139EAC8AC9E5DF615B7418B" xlink:to="loc_us-gaap_IncomeTaxDisclosureAbstract_0A667AD910A0548399745DF615BF8AE9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_DeferredTaxAssetsLiabilitiesNetCurrent" xlink:label="loc_us-gaap_DeferredTaxAssetsLiabilitiesNetCurrent_13FFA3DB2136151777515DF615BFCD45" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxDisclosureAbstract_0A667AD910A0548399745DF615BF8AE9" xlink:to="loc_us-gaap_DeferredTaxAssetsLiabilitiesNetCurrent_13FFA3DB2136151777515DF615BFCD45" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_DeferredTaxAssetsLiabilitiesNetNoncurrent" xlink:label="loc_us-gaap_DeferredTaxAssetsLiabilitiesNetNoncurrent_C5C3E105F179FAC2F4965DF615BF4652" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxDisclosureAbstract_0A667AD910A0548399745DF615BF8AE9" xlink:to="loc_us-gaap_DeferredTaxAssetsLiabilitiesNetNoncurrent_C5C3E105F179FAC2F4965DF615BF4652" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption" xlink:label="loc_us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption_4AA67F0027C346BA68235DFA724CFF29" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_D0C42E537139EAC8AC9E5DF615B7418B" xlink:to="loc_us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption_4AA67F0027C346BA68235DFA724CFF29" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.qualys.com/role/CompanyAndSummaryOfSignificantAccountingPoliciesPolicies" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.qualys.com/role/ConsolidatedBalanceSheets" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.qualys.com/role/ConsolidatedBalanceSheetsParenthetical" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.qualys.com/role/ConsolidatedStatementsOfCashFlows" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.qualys.com/role/ConsolidatedStatementsOfComprehensiveIncome" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.qualys.com/role/ConsolidatedStatementsOfOperations" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.qualys.com/role/ConsolidatedStatementsOfStockholdersEquity" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_AF2F203EEF21B30C96036C6563E5E13B" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_5CF16D8A533BD7AAC36D6C6563E2DAFD" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_AF2F203EEF21B30C96036C6563E5E13B" xlink:to="loc_us-gaap_StatementTable_5CF16D8A533BD7AAC36D6C6563E2DAFD" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_EBEA3F80B0116FA78C856C6563E2428E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_5CF16D8A533BD7AAC36D6C6563E2DAFD" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_EBEA3F80B0116FA78C856C6563E2428E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_27542F07FE90A08E83C76C6563E267AE_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_EBEA3F80B0116FA78C856C6563E2428E" xlink:to="loc_us-gaap_EquityComponentDomain_27542F07FE90A08E83C76C6563E267AE_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_27542F07FE90A08E83C76C6563E267AE" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_EBEA3F80B0116FA78C856C6563E2428E" xlink:to="loc_us-gaap_EquityComponentDomain_27542F07FE90A08E83C76C6563E267AE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_CommonStockMember" xlink:label="loc_us-gaap_CommonStockMember_E19281A9E3A930C36E246C6563E2BCC5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_27542F07FE90A08E83C76C6563E267AE" xlink:to="loc_us-gaap_CommonStockMember_E19281A9E3A930C36E246C6563E2BCC5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AdditionalPaidInCapitalMember" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_D7B9B0F601652E43223B6C6563E5394B" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_27542F07FE90A08E83C76C6563E267AE" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_D7B9B0F601652E43223B6C6563E5394B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_3CEC837B68FC289A665B6C6563E58382" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_27542F07FE90A08E83C76C6563E267AE" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_3CEC837B68FC289A665B6C6563E58382" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_RetainedEarningsMember" xlink:label="loc_us-gaap_RetainedEarningsMember_DAC7CC7F02F23D9B9B1B6C6563E5B8FD" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_27542F07FE90A08E83C76C6563E267AE" xlink:to="loc_us-gaap_RetainedEarningsMember_DAC7CC7F02F23D9B9B1B6C6563E5B8FD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_183EF1F93C06B1C12A356C6563E52FF1" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_AF2F203EEF21B30C96036C6563E5E13B" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_183EF1F93C06B1C12A356C6563E52FF1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_StockholdersEquity" xlink:label="loc_us-gaap_StockholdersEquity_862273691AD9CCFE93266C6563E5B5EE" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_183EF1F93C06B1C12A356C6563E52FF1" xlink:to="loc_us-gaap_StockholdersEquity_862273691AD9CCFE93266C6563E5B5EE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_SharesOutstanding" xlink:label="loc_us-gaap_SharesOutstanding_0B2E0C40C8A8BD7D14F66C6563E5A801" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_183EF1F93C06B1C12A356C6563E52FF1" xlink:to="loc_us-gaap_SharesOutstanding_0B2E0C40C8A8BD7D14F66C6563E5A801" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_NetIncomeLoss" xlink:label="loc_us-gaap_NetIncomeLoss_8B3D0D49817F5411D9E86C6563E5EC67" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_183EF1F93C06B1C12A356C6563E52FF1" xlink:to="loc_us-gaap_NetIncomeLoss_8B3D0D49817F5411D9E86C6563E5EC67" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax_B6E0EF1C9A2C7DE9EBD86C6563E51E09" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_183EF1F93C06B1C12A356C6563E52FF1" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax_B6E0EF1C9A2C7DE9EBD86C6563E51E09" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_44D95136E3FFD5B28B156C6563E5DBA4" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_183EF1F93C06B1C12A356C6563E52FF1" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_44D95136E3FFD5B28B156C6563E5DBA4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_84C7A780F9F6CDCB72236C6563E52F07" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_183EF1F93C06B1C12A356C6563E52FF1" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_84C7A780F9F6CDCB72236C6563E52F07" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_StockIssuedDuringPeriodValueRestrictedStockAwardVested" xlink:label="loc_qlys_StockIssuedDuringPeriodValueRestrictedStockAwardVested_9558EE2874EC328918D56C6563E6CD14" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_183EF1F93C06B1C12A356C6563E52FF1" xlink:to="loc_qlys_StockIssuedDuringPeriodValueRestrictedStockAwardVested_9558EE2874EC328918D56C6563E6CD14" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_StockIssuedDuringPeriodSharesRestrictedStockAwardVested" xlink:label="loc_qlys_StockIssuedDuringPeriodSharesRestrictedStockAwardVested_9B8B5D050BB8730C7CF16C6563E61B7F" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_183EF1F93C06B1C12A356C6563E52FF1" xlink:to="loc_qlys_StockIssuedDuringPeriodSharesRestrictedStockAwardVested_9B8B5D050BB8730C7CF16C6563E61B7F" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_AdjustmentsToAdditionalPaidInCapitalShareBasedCompensationStockOptionsRequisiteServicePeriodRecognitionEarlyExercised" xlink:label="loc_qlys_AdjustmentsToAdditionalPaidInCapitalShareBasedCompensationStockOptionsRequisiteServicePeriodRecognitionEarlyExercised_1DCF7E72E3FC9BFBC1276C6563E68B5B" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_183EF1F93C06B1C12A356C6563E52FF1" xlink:to="loc_qlys_AdjustmentsToAdditionalPaidInCapitalShareBasedCompensationStockOptionsRequisiteServicePeriodRecognitionEarlyExercised_1DCF7E72E3FC9BFBC1276C6563E68B5B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalTaxEffectFromShareBasedCompensation" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalTaxEffectFromShareBasedCompensation_C05FB164A3171E5C86D66C6563E6CC6C" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_183EF1F93C06B1C12A356C6563E52FF1" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalTaxEffectFromShareBasedCompensation_C05FB164A3171E5C86D66C6563E6CC6C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_StockRepurchasedDuringPeriodValue" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodValue_409596D06259FA4C07686C6563E65E6D" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_183EF1F93C06B1C12A356C6563E52FF1" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodValue_409596D06259FA4C07686C6563E65E6D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_StockRepurchasedDuringPeriodShares" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodShares_FBF139C76805E946C36B6C6563E679E2" xlink:type="locator" />
    <link:definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_183EF1F93C06B1C12A356C6563E52FF1" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodShares_FBF139C76805E946C36B6C6563E679E2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueIssuedForServices" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueIssuedForServices_DF041395276BBCBAE3146C6563E647A7" xlink:type="locator" />
    <link:definitionArc order="13" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_183EF1F93C06B1C12A356C6563E52FF1" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueIssuedForServices_DF041395276BBCBAE3146C6563E647A7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesIssuedForServices" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesIssuedForServices_FFCBE571216A8C0559EE6C6563E6DE1D" xlink:type="locator" />
    <link:definitionArc order="14" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_183EF1F93C06B1C12A356C6563E52FF1" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesIssuedForServices_FFCBE571216A8C0559EE6C6563E6DE1D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalShareBasedCompensationRestrictedStockUnitsRequisiteServicePeriodRecognition" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalShareBasedCompensationRestrictedStockUnitsRequisiteServicePeriodRecognition_DB45DCD0F9F40FD15F9C6C6563E61377" xlink:type="locator" />
    <link:definitionArc order="15" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_183EF1F93C06B1C12A356C6563E52FF1" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalShareBasedCompensationRestrictedStockUnitsRequisiteServicePeriodRecognition_DB45DCD0F9F40FD15F9C6C6563E61377" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_81A906FD39BDE76DD3896C6563E60B5A" xlink:type="locator" />
    <link:definitionArc order="16" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_183EF1F93C06B1C12A356C6563E52FF1" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_81A906FD39BDE76DD3896C6563E60B5A" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.qualys.com/role/DocumentAndEntityInformation" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.qualys.com/role/EmployeeStockAndBenefitPlans" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.qualys.com/role/EmployeeStockAndBenefitPlansCommonStockAndPreferredStockDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_D83A4150F7F05A6D7CA25E095E4AB904" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_C78680E247A89B406CBA5E095E3D3881" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_D83A4150F7F05A6D7CA25E095E4AB904" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_C78680E247A89B406CBA5E095E3D3881" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_PlanNameAxis" xlink:label="loc_us-gaap_PlanNameAxis_B51496420E69BA6647AD5E0B5536D1BC" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_C78680E247A89B406CBA5E095E3D3881" xlink:to="loc_us-gaap_PlanNameAxis_B51496420E69BA6647AD5E0B5536D1BC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_PlanNameDomain" xlink:label="loc_us-gaap_PlanNameDomain_0A8BAB4080A60E334E565E0B55385BE5_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_B51496420E69BA6647AD5E0B5536D1BC" xlink:to="loc_us-gaap_PlanNameDomain_0A8BAB4080A60E334E565E0B55385BE5_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_PlanNameDomain" xlink:label="loc_us-gaap_PlanNameDomain_0A8BAB4080A60E334E565E0B55385BE5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_B51496420E69BA6647AD5E0B5536D1BC" xlink:to="loc_us-gaap_PlanNameDomain_0A8BAB4080A60E334E565E0B55385BE5" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_A2000EquityIncentivePlanMember" xlink:label="loc_qlys_A2000EquityIncentivePlanMember_13C381210B43A31D8AEC5E0B55382F3E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_0A8BAB4080A60E334E565E0B55385BE5" xlink:to="loc_qlys_A2000EquityIncentivePlanMember_13C381210B43A31D8AEC5E0B55382F3E" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_A2012EquityIncentivePlanMember" xlink:label="loc_qlys_A2012EquityIncentivePlanMember_CB02C6951C823F39BB2B5E0B55381368" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_0A8BAB4080A60E334E565E0B55385BE5" xlink:to="loc_qlys_A2012EquityIncentivePlanMember_CB02C6951C823F39BB2B5E0B55381368" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="loc_us-gaap_StatementClassOfStockAxis_9C6A82261C1F439759F15E0BE9B2FD29" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_C78680E247A89B406CBA5E095E3D3881" xlink:to="loc_us-gaap_StatementClassOfStockAxis_9C6A82261C1F439759F15E0BE9B2FD29" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_D9B32EFA2E9A09D210F25E0BE9B861CE_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_9C6A82261C1F439759F15E0BE9B2FD29" xlink:to="loc_us-gaap_ClassOfStockDomain_D9B32EFA2E9A09D210F25E0BE9B861CE_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_D9B32EFA2E9A09D210F25E0BE9B861CE" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_9C6A82261C1F439759F15E0BE9B2FD29" xlink:to="loc_us-gaap_ClassOfStockDomain_D9B32EFA2E9A09D210F25E0BE9B861CE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_PreferredStockMember" xlink:label="loc_us-gaap_PreferredStockMember_32A49E69D2D76609EE595E0BE9B956CC" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_D9B32EFA2E9A09D210F25E0BE9B861CE" xlink:to="loc_us-gaap_PreferredStockMember_32A49E69D2D76609EE595E0BE9B956CC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_D91FA6416A46E6B8CE6A5E0B801DA5AC" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_D83A4150F7F05A6D7CA25E095E4AB904" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_D91FA6416A46E6B8CE6A5E0B801DA5AC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_794B065F51E65ED438A25E0B8025186C" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_D83A4150F7F05A6D7CA25E095E4AB904" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_794B065F51E65ED438A25E0B8025186C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_CommonStockCapitalSharesReservedForFutureIssuance" xlink:label="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_65E21F5C48EAB8C9365D5E0A24A0213C" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_D83A4150F7F05A6D7CA25E095E4AB904" xlink:to="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_65E21F5C48EAB8C9365D5E0A24A0213C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_PreferredStockNumberOfSharesParValueAndOtherDisclosuresAbstract" xlink:label="loc_us-gaap_PreferredStockNumberOfSharesParValueAndOtherDisclosuresAbstract_102AB93AE5A2C0E7086C5E0BD3F297FC" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_D83A4150F7F05A6D7CA25E095E4AB904" xlink:to="loc_us-gaap_PreferredStockNumberOfSharesParValueAndOtherDisclosuresAbstract_102AB93AE5A2C0E7086C5E0BD3F297FC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_PreferredStockSharesAuthorized" xlink:label="loc_us-gaap_PreferredStockSharesAuthorized_E23A545C1447166D61125E0BC4C4BD17" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PreferredStockNumberOfSharesParValueAndOtherDisclosuresAbstract_102AB93AE5A2C0E7086C5E0BD3F297FC" xlink:to="loc_us-gaap_PreferredStockSharesAuthorized_E23A545C1447166D61125E0BC4C4BD17" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_PreferredStockParOrStatedValuePerShare" xlink:label="loc_us-gaap_PreferredStockParOrStatedValuePerShare_481E74CAB208FE7D71665E0BC4CE882D" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PreferredStockNumberOfSharesParValueAndOtherDisclosuresAbstract_102AB93AE5A2C0E7086C5E0BD3F297FC" xlink:to="loc_us-gaap_PreferredStockParOrStatedValuePerShare_481E74CAB208FE7D71665E0BC4CE882D" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.qualys.com/role/EmployeeStockAndBenefitPlansExpenseDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_2E6A7BF3AC1B930B30C461ECAECCA20F" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable" xlink:label="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_0880981D39B56D8AADF561ECAEC602F0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_2E6A7BF3AC1B930B30C461ECAECCA20F" xlink:to="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_0880981D39B56D8AADF561ECAEC602F0" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_IncomeStatementLocationAxis" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_B52602F12CC58ABFCFF261ECAEC6EEB4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_0880981D39B56D8AADF561ECAEC602F0" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_B52602F12CC58ABFCFF261ECAEC6EEB4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_6C8238C29488F7424EFF61ECAEC685D6_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_B52602F12CC58ABFCFF261ECAEC6EEB4" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_6C8238C29488F7424EFF61ECAEC685D6_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_6C8238C29488F7424EFF61ECAEC685D6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_B52602F12CC58ABFCFF261ECAEC6EEB4" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_6C8238C29488F7424EFF61ECAEC685D6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_CostOfSalesMember" xlink:label="loc_us-gaap_CostOfSalesMember_A61AD1831BF19C28D93D61ECAEC664E6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_6C8238C29488F7424EFF61ECAEC685D6" xlink:to="loc_us-gaap_CostOfSalesMember_A61AD1831BF19C28D93D61ECAEC664E6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ResearchAndDevelopmentExpenseMember" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpenseMember_BA720EC1344800217DBE61ECAEC6BC79" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_6C8238C29488F7424EFF61ECAEC685D6" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpenseMember_BA720EC1344800217DBE61ECAEC6BC79" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_SellingAndMarketingExpenseMember" xlink:label="loc_us-gaap_SellingAndMarketingExpenseMember_896737484A8E306B605E61ECAECBBB59" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_6C8238C29488F7424EFF61ECAEC685D6" xlink:to="loc_us-gaap_SellingAndMarketingExpenseMember_896737484A8E306B605E61ECAECBBB59" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_GeneralAndAdministrativeExpenseMember" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpenseMember_83C06E32B637F6F73F7E61ECAECC92FC" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_6C8238C29488F7424EFF61ECAEC685D6" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpenseMember_83C06E32B637F6F73F7E61ECAECC92FC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaap_AwardTypeAxis_68C799A35BB8F5DE08AF61FE7B789A9A" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_0880981D39B56D8AADF561ECAEC602F0" xlink:to="loc_us-gaap_AwardTypeAxis_68C799A35BB8F5DE08AF61FE7B789A9A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_23C00B41B38F4886A77861FE7B9B10F9_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_68C799A35BB8F5DE08AF61FE7B789A9A" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_23C00B41B38F4886A77861FE7B9B10F9_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_23C00B41B38F4886A77861FE7B9B10F9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_68C799A35BB8F5DE08AF61FE7B789A9A" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_23C00B41B38F4886A77861FE7B9B10F9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_RestrictedStockUnitsRSUMember" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_0586BA3028621D890BF661FFE5EDDEBE" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_23C00B41B38F4886A77861FE7B9B10F9" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_0586BA3028621D890BF661FFE5EDDEBE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AllocatedShareBasedCompensationExpense" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_D93A493D2085DDAE332B61ECAECCFE56" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_2E6A7BF3AC1B930B30C461ECAECCA20F" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_D93A493D2085DDAE332B61ECAECCFE56" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_9ED12A13D987B8D6E81561ECAECCF90F" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_2E6A7BF3AC1B930B30C461ECAECCA20F" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_9ED12A13D987B8D6E81561ECAECCF90F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_39DA8A0ADB17434CCDA961ECAECCE288" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_2E6A7BF3AC1B930B30C461ECAECCA20F" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_39DA8A0ADB17434CCDA961ECAECCE288" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_IssuanceOfStockAndWarrantsForServicesOrClaims" xlink:label="loc_us-gaap_IssuanceOfStockAndWarrantsForServicesOrClaims_44A881F3548061E376C861ECAECC9AAA" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_2E6A7BF3AC1B930B30C461ECAECCA20F" xlink:to="loc_us-gaap_IssuanceOfStockAndWarrantsForServicesOrClaims_44A881F3548061E376C861ECAECC9AAA" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.qualys.com/role/EmployeeStockAndBenefitPlansFairValueAssumptionsStockOptionsDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_687D142CD8F5D4E967894A7B846E6BB6" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_F3E56989302A6D75EA954A7B846D7351" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_687D142CD8F5D4E967894A7B846E6BB6" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_F3E56989302A6D75EA954A7B846D7351" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_RangeAxis" xlink:label="loc_us-gaap_RangeAxis_552B2F9C2CA2F66469884A7B846DAF8E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_F3E56989302A6D75EA954A7B846D7351" xlink:to="loc_us-gaap_RangeAxis_552B2F9C2CA2F66469884A7B846DAF8E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_D5029B4C3BF29F2B43914A7B846D4D68_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RangeAxis_552B2F9C2CA2F66469884A7B846DAF8E" xlink:to="loc_us-gaap_RangeMember_D5029B4C3BF29F2B43914A7B846D4D68_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_D5029B4C3BF29F2B43914A7B846D4D68" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RangeAxis_552B2F9C2CA2F66469884A7B846DAF8E" xlink:to="loc_us-gaap_RangeMember_D5029B4C3BF29F2B43914A7B846D4D68" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_MinimumMember" xlink:label="loc_us-gaap_MinimumMember_17921D340C6293823A524A7B846DBFBA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_D5029B4C3BF29F2B43914A7B846D4D68" xlink:to="loc_us-gaap_MinimumMember_17921D340C6293823A524A7B846DBFBA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_MaximumMember" xlink:label="loc_us-gaap_MaximumMember_0624D3E1F5230D1421864A7B846D17B4" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_D5029B4C3BF29F2B43914A7B846D4D68" xlink:to="loc_us-gaap_MaximumMember_0624D3E1F5230D1421864A7B846D17B4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaap_AwardTypeAxis_F8004D6DBD3A5E58232D4A7B846D6E3C" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_F3E56989302A6D75EA954A7B846D7351" xlink:to="loc_us-gaap_AwardTypeAxis_F8004D6DBD3A5E58232D4A7B846D6E3C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_FE11760DCEC643915CAB4A7B846DF9E9_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_F8004D6DBD3A5E58232D4A7B846D6E3C" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_FE11760DCEC643915CAB4A7B846DF9E9_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_FE11760DCEC643915CAB4A7B846DF9E9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_F8004D6DBD3A5E58232D4A7B846D6E3C" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_FE11760DCEC643915CAB4A7B846DF9E9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="loc_us-gaap_EmployeeStockOptionMember_31CE72194EB6AB60E4DA4A7B846E24EB" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_FE11760DCEC643915CAB4A7B846DF9E9" xlink:to="loc_us-gaap_EmployeeStockOptionMember_31CE72194EB6AB60E4DA4A7B846E24EB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_45814D95CBA78C5A0D124A7B846E2295" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_687D142CD8F5D4E967894A7B846E6BB6" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_45814D95CBA78C5A0D124A7B846E2295" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_9D4849B67B6D4DB166144A7B846EF3AB" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_687D142CD8F5D4E967894A7B846E6BB6" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_9D4849B67B6D4DB166144A7B846EF3AB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_86BAB31EF83C57E36A8D4A7B846E47BC" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_687D142CD8F5D4E967894A7B846E6BB6" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_86BAB31EF83C57E36A8D4A7B846E47BC" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_2CB655F620DD2F68B3164A7B846E53CB" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_687D142CD8F5D4E967894A7B846E6BB6" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_2CB655F620DD2F68B3164A7B846E53CB" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.qualys.com/role/EmployeeStockAndBenefitPlansOptionsOutstandingAndVestedDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems" xlink:label="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_AAA078FE8FE809266D8E61ECAE7B8034" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeTable" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeTable_46B4E887621A8D48670361ECAE7474DF" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_AAA078FE8FE809266D8E61ECAE7B8034" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeTable_46B4E887621A8D48670361ECAE7474DF" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_PlanNameAxis" xlink:label="loc_us-gaap_PlanNameAxis_5546C252711EAAF6855861ECAE740895" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeTable_46B4E887621A8D48670361ECAE7474DF" xlink:to="loc_us-gaap_PlanNameAxis_5546C252711EAAF6855861ECAE740895" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_PlanNameDomain" xlink:label="loc_us-gaap_PlanNameDomain_5B21AF8B1AEF1ECA854261ECAE7456BC_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_5546C252711EAAF6855861ECAE740895" xlink:to="loc_us-gaap_PlanNameDomain_5B21AF8B1AEF1ECA854261ECAE7456BC_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_PlanNameDomain" xlink:label="loc_us-gaap_PlanNameDomain_5B21AF8B1AEF1ECA854261ECAE7456BC" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_5546C252711EAAF6855861ECAE740895" xlink:to="loc_us-gaap_PlanNameDomain_5B21AF8B1AEF1ECA854261ECAE7456BC" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_A2000EquityIncentivePlanMember" xlink:label="loc_qlys_A2000EquityIncentivePlanMember_03A51FE142E45EC1DB1061ECAE74E4A1" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_5B21AF8B1AEF1ECA854261ECAE7456BC" xlink:to="loc_qlys_A2000EquityIncentivePlanMember_03A51FE142E45EC1DB1061ECAE74E4A1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis" xlink:label="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis_9516A6FC0509B60EC49261ECAE741B2D" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeTable_46B4E887621A8D48670361ECAE7474DF" xlink:to="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis_9516A6FC0509B60EC49261ECAE741B2D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain" xlink:label="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_FB05BD1799D77567253961ECAE746E62_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis_9516A6FC0509B60EC49261ECAE741B2D" xlink:to="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_FB05BD1799D77567253961ECAE746E62_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain" xlink:label="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_FB05BD1799D77567253961ECAE746E62" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis_9516A6FC0509B60EC49261ECAE741B2D" xlink:to="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_FB05BD1799D77567253961ECAE746E62" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_ExercisePriceRangeOneMember" xlink:label="loc_qlys_ExercisePriceRangeOneMember_48A5B70C643B09C6312D61ECAE74F4C7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_FB05BD1799D77567253961ECAE746E62" xlink:to="loc_qlys_ExercisePriceRangeOneMember_48A5B70C643B09C6312D61ECAE74F4C7" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_ExercisePriceRangeTwoMember" xlink:label="loc_qlys_ExercisePriceRangeTwoMember_5DD324D96625860650C361ECAE75566F" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_FB05BD1799D77567253961ECAE746E62" xlink:to="loc_qlys_ExercisePriceRangeTwoMember_5DD324D96625860650C361ECAE75566F" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_ExercisePriceRangeThreeMember" xlink:label="loc_qlys_ExercisePriceRangeThreeMember_0A76833F91BBA76AF68C61ECAE755220" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_FB05BD1799D77567253961ECAE746E62" xlink:to="loc_qlys_ExercisePriceRangeThreeMember_0A76833F91BBA76AF68C61ECAE755220" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_ExercisePriceRangeFourMember" xlink:label="loc_qlys_ExercisePriceRangeFourMember_E08228425A2163F4E0A361ECAE75F7A3" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_FB05BD1799D77567253961ECAE746E62" xlink:to="loc_qlys_ExercisePriceRangeFourMember_E08228425A2163F4E0A361ECAE75F7A3" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_ExercisePriceRangeFiveMember" xlink:label="loc_qlys_ExercisePriceRangeFiveMember_720C716EC4A71050CBCF61ECAE75FF08" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_FB05BD1799D77567253961ECAE746E62" xlink:to="loc_qlys_ExercisePriceRangeFiveMember_720C716EC4A71050CBCF61ECAE75FF08" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_ExercisePriceRangeSixMember" xlink:label="loc_qlys_ExercisePriceRangeSixMember_C30650EE359CDFF94B5D61ECAE751EF4" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_FB05BD1799D77567253961ECAE746E62" xlink:to="loc_qlys_ExercisePriceRangeSixMember_C30650EE359CDFF94B5D61ECAE751EF4" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_ExercisePriceRangeSevenMember" xlink:label="loc_qlys_ExercisePriceRangeSevenMember_62B008E6124C0B6E8E3F61ECAE750273" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_FB05BD1799D77567253961ECAE746E62" xlink:to="loc_qlys_ExercisePriceRangeSevenMember_62B008E6124C0B6E8E3F61ECAE750273" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_ExercisePriceRangeEightMember" xlink:label="loc_qlys_ExercisePriceRangeEightMember_3B4B509745B0C8F6CDB961ECAE7A2A08" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_FB05BD1799D77567253961ECAE746E62" xlink:to="loc_qlys_ExercisePriceRangeEightMember_3B4B509745B0C8F6CDB961ECAE7A2A08" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_ExercisePriceRangeNineMember" xlink:label="loc_qlys_ExercisePriceRangeNineMember_5508B2FF69C33C4272CC61ECAE7A53F3" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_FB05BD1799D77567253961ECAE746E62" xlink:to="loc_qlys_ExercisePriceRangeNineMember_5508B2FF69C33C4272CC61ECAE7A53F3" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_ExercisePriceRangeTenMember" xlink:label="loc_qlys_ExercisePriceRangeTenMember_FA54B2EF0DB5CF88A1F861ECAE7BC227" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_FB05BD1799D77567253961ECAE746E62" xlink:to="loc_qlys_ExercisePriceRangeTenMember_FA54B2EF0DB5CF88A1F861ECAE7BC227" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaap_AwardTypeAxis_AEE506E8DE2012ECCF5F61ECAE7BD904" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeTable_46B4E887621A8D48670361ECAE7474DF" xlink:to="loc_us-gaap_AwardTypeAxis_AEE506E8DE2012ECCF5F61ECAE7BD904" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_74592BA8B1E32B0D2C4761ECAE7B5F55_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_AEE506E8DE2012ECCF5F61ECAE7BD904" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_74592BA8B1E32B0D2C4761ECAE7B5F55_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_74592BA8B1E32B0D2C4761ECAE7B5F55" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_AEE506E8DE2012ECCF5F61ECAE7BD904" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_74592BA8B1E32B0D2C4761ECAE7B5F55" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="loc_us-gaap_EmployeeStockOptionMember_26E3A2F44F35ED2F8D0061ECAE7B2B2F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_74592BA8B1E32B0D2C4761ECAE7B5F55" xlink:to="loc_us-gaap_EmployeeStockOptionMember_26E3A2F44F35ED2F8D0061ECAE7B2B2F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit" xlink:label="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit_210C250984FE5B97D76261ECAE7B7D70" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_AAA078FE8FE809266D8E61ECAE7B8034" xlink:to="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit_210C250984FE5B97D76261ECAE7B7D70" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit" xlink:label="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit_A0A860002EEB2C0B03E061ECAE7BE87A" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_AAA078FE8FE809266D8E61ECAE7B8034" xlink:to="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit_A0A860002EEB2C0B03E061ECAE7BE87A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingOptions" xlink:label="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingOptions_AEF02ACDE4B109E16A8561ECAE7B1FA5" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_AAA078FE8FE809266D8E61ECAE7B8034" xlink:to="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingOptions_AEF02ACDE4B109E16A8561ECAE7B1FA5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageExercisePriceBeginningBalance1" xlink:label="loc_us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageExercisePriceBeginningBalance1_7F9B9020DEDC4BAC1B6261ECAE7CF16B" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_AAA078FE8FE809266D8E61ECAE7B8034" xlink:to="loc_us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageExercisePriceBeginningBalance1_7F9B9020DEDC4BAC1B6261ECAE7CF16B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageRemainingContractualTerm2" xlink:label="loc_us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageRemainingContractualTerm2_F804E62825258283877061ECAE7C303A" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_AAA078FE8FE809266D8E61ECAE7B8034" xlink:to="loc_us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageRemainingContractualTerm2_F804E62825258283877061ECAE7C303A" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfVestedOptions" xlink:label="loc_qlys_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfVestedOptions_3A1C6FEF89015E5392E161ECAE7CAF86" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_AAA078FE8FE809266D8E61ECAE7B8034" xlink:to="loc_qlys_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfVestedOptions_3A1C6FEF89015E5392E161ECAE7CAF86" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeVestedOptionsWeightedAverageExercisePrice" xlink:label="loc_qlys_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeVestedOptionsWeightedAverageExercisePrice_6C9E6EC9B7E779BB2A5561ECAE7C3A2C" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_AAA078FE8FE809266D8E61ECAE7B8034" xlink:to="loc_qlys_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeVestedOptionsWeightedAverageExercisePrice_6C9E6EC9B7E779BB2A5561ECAE7C3A2C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_BDC4FC03F5695356816A61ECAE7C8469" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_AAA078FE8FE809266D8E61ECAE7B8034" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_BDC4FC03F5695356816A61ECAE7C8469" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantedInPeriodTotalFairValue" xlink:label="loc_qlys_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantedInPeriodTotalFairValue_C9D30E2041E017722FD061ECAE7C6693" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_AAA078FE8FE809266D8E61ECAE7B8034" xlink:to="loc_qlys_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantedInPeriodTotalFairValue_C9D30E2041E017722FD061ECAE7C6693" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue_DDC7341564D5922D656261ECAE7C16F2" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_AAA078FE8FE809266D8E61ECAE7B8034" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue_DDC7341564D5922D656261ECAE7C16F2" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.qualys.com/role/EmployeeStockAndBenefitPlansPlanInformationDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_AD6C79412C271ABE87486DED2962641E" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_19B16BF27ACC42322E2C6DED295F9B19" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_AD6C79412C271ABE87486DED2962641E" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_19B16BF27ACC42322E2C6DED295F9B19" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_EquityIncentivePlanAnnualIncreaseFeatureAxis" xlink:label="loc_qlys_EquityIncentivePlanAnnualIncreaseFeatureAxis_BEB6160B13AFB4323D8A6DED296039B9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_19B16BF27ACC42322E2C6DED295F9B19" xlink:to="loc_qlys_EquityIncentivePlanAnnualIncreaseFeatureAxis_BEB6160B13AFB4323D8A6DED296039B9" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_EquityIncentivePlanAnnualIncreaseFeatureDomain" xlink:label="loc_qlys_EquityIncentivePlanAnnualIncreaseFeatureDomain_7A68ACDCAA1DDBC106876DED29606824_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_qlys_EquityIncentivePlanAnnualIncreaseFeatureAxis_BEB6160B13AFB4323D8A6DED296039B9" xlink:to="loc_qlys_EquityIncentivePlanAnnualIncreaseFeatureDomain_7A68ACDCAA1DDBC106876DED29606824_default" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_EquityIncentivePlanAnnualIncreaseFeatureDomain" xlink:label="loc_qlys_EquityIncentivePlanAnnualIncreaseFeatureDomain_7A68ACDCAA1DDBC106876DED29606824" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_qlys_EquityIncentivePlanAnnualIncreaseFeatureAxis_BEB6160B13AFB4323D8A6DED296039B9" xlink:to="loc_qlys_EquityIncentivePlanAnnualIncreaseFeatureDomain_7A68ACDCAA1DDBC106876DED29606824" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_IncreaseOfNumberOfSharesOptionMember" xlink:label="loc_qlys_IncreaseOfNumberOfSharesOptionMember_1395946AE73B640B4A3D6DED296015FB" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_qlys_EquityIncentivePlanAnnualIncreaseFeatureDomain_7A68ACDCAA1DDBC106876DED29606824" xlink:to="loc_qlys_IncreaseOfNumberOfSharesOptionMember_1395946AE73B640B4A3D6DED296015FB" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_IncreaseOfPercentageOfSharesOutstandingOptionMember" xlink:label="loc_qlys_IncreaseOfPercentageOfSharesOutstandingOptionMember_C60B7F39021E005E67A26DED2960852C" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_qlys_EquityIncentivePlanAnnualIncreaseFeatureDomain_7A68ACDCAA1DDBC106876DED29606824" xlink:to="loc_qlys_IncreaseOfPercentageOfSharesOutstandingOptionMember_C60B7F39021E005E67A26DED2960852C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_PlanNameAxis" xlink:label="loc_us-gaap_PlanNameAxis_AC14940B47FC19B22DE26DED2961F161" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_19B16BF27ACC42322E2C6DED295F9B19" xlink:to="loc_us-gaap_PlanNameAxis_AC14940B47FC19B22DE26DED2961F161" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_PlanNameDomain" xlink:label="loc_us-gaap_PlanNameDomain_C1D2FA1CD77EE8F5D00A6DED296145CC_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_AC14940B47FC19B22DE26DED2961F161" xlink:to="loc_us-gaap_PlanNameDomain_C1D2FA1CD77EE8F5D00A6DED296145CC_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_PlanNameDomain" xlink:label="loc_us-gaap_PlanNameDomain_C1D2FA1CD77EE8F5D00A6DED296145CC" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_AC14940B47FC19B22DE26DED2961F161" xlink:to="loc_us-gaap_PlanNameDomain_C1D2FA1CD77EE8F5D00A6DED296145CC" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_A2012EquityIncentivePlanMember" xlink:label="loc_qlys_A2012EquityIncentivePlanMember_BE62DDFDCC822F4465CE6DED29610735" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_C1D2FA1CD77EE8F5D00A6DED296145CC" xlink:to="loc_qlys_A2012EquityIncentivePlanMember_BE62DDFDCC822F4465CE6DED29610735" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_A2000EquityIncentivePlanMember" xlink:label="loc_qlys_A2000EquityIncentivePlanMember_B473EE8CF47DDBC1D8B36DED2961BA52" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_C1D2FA1CD77EE8F5D00A6DED296145CC" xlink:to="loc_qlys_A2000EquityIncentivePlanMember_B473EE8CF47DDBC1D8B36DED2961BA52" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaap_AwardTypeAxis_FC8BD27C68CC556595DB6DED2961EF40" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_19B16BF27ACC42322E2C6DED295F9B19" xlink:to="loc_us-gaap_AwardTypeAxis_FC8BD27C68CC556595DB6DED2961EF40" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_D0EC1F2BA0813F2354796DED29611950_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_FC8BD27C68CC556595DB6DED2961EF40" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_D0EC1F2BA0813F2354796DED29611950_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_D0EC1F2BA0813F2354796DED29611950" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_FC8BD27C68CC556595DB6DED2961EF40" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_D0EC1F2BA0813F2354796DED29611950" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="loc_us-gaap_EmployeeStockOptionMember_0EC6D77F4BC69DF867536DED29620D46" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_D0EC1F2BA0813F2354796DED29611950" xlink:to="loc_us-gaap_EmployeeStockOptionMember_0EC6D77F4BC69DF867536DED29620D46" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_RangeAxis" xlink:label="loc_us-gaap_RangeAxis_8E789C6028100C37BC916DED29623407" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_19B16BF27ACC42322E2C6DED295F9B19" xlink:to="loc_us-gaap_RangeAxis_8E789C6028100C37BC916DED29623407" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_9B20ADF7FB79620146136DED29625F99_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RangeAxis_8E789C6028100C37BC916DED29623407" xlink:to="loc_us-gaap_RangeMember_9B20ADF7FB79620146136DED29625F99_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_9B20ADF7FB79620146136DED29625F99" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RangeAxis_8E789C6028100C37BC916DED29623407" xlink:to="loc_us-gaap_RangeMember_9B20ADF7FB79620146136DED29625F99" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_MaximumMember" xlink:label="loc_us-gaap_MaximumMember_6E93C632919282C8FE136DED29628628" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_9B20ADF7FB79620146136DED29625F99" xlink:to="loc_us-gaap_MaximumMember_6E93C632919282C8FE136DED29628628" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_MinimumMember" xlink:label="loc_us-gaap_MinimumMember_65AF66803DDCD40AA7826DED29623B4A" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_9B20ADF7FB79620146136DED29625F99" xlink:to="loc_us-gaap_MinimumMember_65AF66803DDCD40AA7826DED29623B4A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_9B2D54227A848114120D6DED2963DFE4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_AD6C79412C271ABE87486DED2962641E" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_9B2D54227A848114120D6DED2963DFE4" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorizedAnnualIncreaseShares" xlink:label="loc_qlys_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorizedAnnualIncreaseShares_65F8E722BB30B5C6D2006DED29634F55" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_AD6C79412C271ABE87486DED2962641E" xlink:to="loc_qlys_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorizedAnnualIncreaseShares_65F8E722BB30B5C6D2006DED29634F55" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorizedAnnualIncreasePercentOfSharesOutstanding" xlink:label="loc_qlys_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorizedAnnualIncreasePercentOfSharesOutstanding_3CBB9847173C6DB732AD6DED2963E9CD" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_AD6C79412C271ABE87486DED2962641E" xlink:to="loc_qlys_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorizedAnnualIncreasePercentOfSharesOutstanding_3CBB9847173C6DB732AD6DED2963E9CD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_2A314C2BF883113264716DED29635738" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_AD6C79412C271ABE87486DED2962641E" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_2A314C2BF883113264716DED29635738" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_ShareBasedCompensationArrangementByShareBasedPaymentAwardTermOfAward" xlink:label="loc_qlys_ShareBasedCompensationArrangementByShareBasedPaymentAwardTermOfAward_940D6CC51AB3309700136DED29638805" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_AD6C79412C271ABE87486DED2962641E" xlink:to="loc_qlys_ShareBasedCompensationArrangementByShareBasedPaymentAwardTermOfAward_940D6CC51AB3309700136DED29638805" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_52AC9EDF8A7CCF85F8016DED2963B57F" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_AD6C79412C271ABE87486DED2962641E" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_52AC9EDF8A7CCF85F8016DED2963B57F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_00B9E08186C9EED5F4416DED2964878D" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_AD6C79412C271ABE87486DED2962641E" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_00B9E08186C9EED5F4416DED2964878D" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardStrikePriceAsPercentageOfMarketValue" xlink:label="loc_qlys_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardStrikePriceAsPercentageOfMarketValue_B9FE10900E94B0C0C6A16DED29642C6D" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_AD6C79412C271ABE87486DED2962641E" xlink:to="loc_qlys_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardStrikePriceAsPercentageOfMarketValue_B9FE10900E94B0C0C6A16DED29642C6D" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForIssuance" xlink:label="loc_qlys_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForIssuance_AC478E7B4D4FA461F57E6DED2964901B" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_AD6C79412C271ABE87486DED2962641E" xlink:to="loc_qlys_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForIssuance_AC478E7B4D4FA461F57E6DED2964901B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_DefinedBenefitPlanContributionsByEmployer" xlink:label="loc_us-gaap_DefinedBenefitPlanContributionsByEmployer_40C837588545D85DF28A6DED2964894E" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_AD6C79412C271ABE87486DED2962641E" xlink:to="loc_us-gaap_DefinedBenefitPlanContributionsByEmployer_40C837588545D85DF28A6DED2964894E" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.qualys.com/role/EmployeeStockAndBenefitPlansRestrictedStockDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5CE35496A4DA15C7F4174A7B840636DF" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_148962AD0F8C81154B114A7B84051CA8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5CE35496A4DA15C7F4174A7B840636DF" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_148962AD0F8C81154B114A7B84051CA8" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaap_AwardTypeAxis_298F7794AFDB1E6750524A7B84065E15" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_148962AD0F8C81154B114A7B84051CA8" xlink:to="loc_us-gaap_AwardTypeAxis_298F7794AFDB1E6750524A7B84065E15" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_32A2961E8F6265D5C07D4A7B8406862E_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_298F7794AFDB1E6750524A7B84065E15" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_32A2961E8F6265D5C07D4A7B8406862E_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_32A2961E8F6265D5C07D4A7B8406862E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_298F7794AFDB1E6750524A7B84065E15" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_32A2961E8F6265D5C07D4A7B8406862E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_RestrictedStockUnitsRSUMember" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_B8084AD463A4063882864A7B84061EAA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_32A2961E8F6265D5C07D4A7B8406862E" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_B8084AD463A4063882864A7B84061EAA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_3016DFB393C9289E8A624A7B8406AB69" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5CE35496A4DA15C7F4174A7B840636DF" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_3016DFB393C9289E8A624A7B8406AB69" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_5221B8B269A20C253EED4A7B840704B2" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5CE35496A4DA15C7F4174A7B840636DF" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_5221B8B269A20C253EED4A7B840704B2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AllocatedShareBasedCompensationExpense" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_0E94C0B4FF0C80977F514A7B8407C09B" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5CE35496A4DA15C7F4174A7B840636DF" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_0E94C0B4FF0C80977F514A7B8407C09B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_03085EFB6788C8447A074A7B8407B30D" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5CE35496A4DA15C7F4174A7B840636DF" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_03085EFB6788C8447A074A7B8407B30D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsForfeituresAndExpirations" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsForfeituresAndExpirations_7E4A588EB0C9403D7AEE4A7B84076A32" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5CE35496A4DA15C7F4174A7B840636DF" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsForfeituresAndExpirations_7E4A588EB0C9403D7AEE4A7B84076A32" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_911ACC78A3E3BAE16CF84A7B8407F403" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5CE35496A4DA15C7F4174A7B840636DF" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_911ACC78A3E3BAE16CF84A7B8407F403" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_97A37F7D5E48D642AC854A7B8407DB71" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5CE35496A4DA15C7F4174A7B840636DF" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_97A37F7D5E48D642AC854A7B8407DB71" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_423B8AA088778303478D4A7B8407C98B" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5CE35496A4DA15C7F4174A7B840636DF" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_423B8AA088778303478D4A7B8407C98B" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.qualys.com/role/EmployeeStockAndBenefitPlansRestrictedStockUnitsAndRestrictedStockAwardsActivityDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_87C27276D4278F38DFA5587A25E5AB71" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_D2B14BDEAE64ADC78951587A25E1379C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_87C27276D4278F38DFA5587A25E5AB71" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_D2B14BDEAE64ADC78951587A25E1379C" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaap_AwardTypeAxis_8AB73D8AEC6C540F82CC587A25E3042E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_D2B14BDEAE64ADC78951587A25E1379C" xlink:to="loc_us-gaap_AwardTypeAxis_8AB73D8AEC6C540F82CC587A25E3042E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_54EF580100B80A073444587A25E331B2_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_8AB73D8AEC6C540F82CC587A25E3042E" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_54EF580100B80A073444587A25E331B2_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_54EF580100B80A073444587A25E331B2" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_8AB73D8AEC6C540F82CC587A25E3042E" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_54EF580100B80A073444587A25E331B2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_RestrictedStockUnitsRSUMember" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_A8F34B803A70DC13403D587B51DB4827" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_54EF580100B80A073444587A25E331B2" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_A8F34B803A70DC13403D587B51DB4827" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_210BB7CD0C2A3AB35A6E587D4CA7AC2A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_87C27276D4278F38DFA5587A25E5AB71" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_210BB7CD0C2A3AB35A6E587D4CA7AC2A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_48393A50695892EC939D587B510DD98E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_210BB7CD0C2A3AB35A6E587D4CA7AC2A" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_48393A50695892EC939D587B510DD98E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_0C739519D6466362C143587B54438ED2" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_210BB7CD0C2A3AB35A6E587D4CA7AC2A" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_0C739519D6466362C143587B54438ED2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_4490D29F4381E98B3D77587B578A2CDB" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_210BB7CD0C2A3AB35A6E587D4CA7AC2A" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_4490D29F4381E98B3D77587B578A2CDB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_B8C4F8A3D95BAB6DCB64587B5AF07BEE" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_210BB7CD0C2A3AB35A6E587D4CA7AC2A" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_B8C4F8A3D95BAB6DCB64587B5AF07BEE" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedAndExpectedToVestOutstandingNumber" xlink:label="loc_qlys_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedAndExpectedToVestOutstandingNumber_7A0CC9ED7BD7661AE68D587BA51ED72D" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_87C27276D4278F38DFA5587A25E5AB71" xlink:to="loc_qlys_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedAndExpectedToVestOutstandingNumber_7A0CC9ED7BD7661AE68D587BA51ED72D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_D8D4BDA3DF93C1218F83587CE5FDDC59" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_87C27276D4278F38DFA5587A25E5AB71" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_D8D4BDA3DF93C1218F83587CE5FDDC59" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_1CBB6D54D24FF313EF52587B52F56F3C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_D8D4BDA3DF93C1218F83587CE5FDDC59" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_1CBB6D54D24FF313EF52587B52F56F3C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_EC584788208AA645BED4587B56367B9B" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_D8D4BDA3DF93C1218F83587CE5FDDC59" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_EC584788208AA645BED4587B56367B9B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_C56F65EE26538CCFE646587B5978A801" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_D8D4BDA3DF93C1218F83587CE5FDDC59" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_C56F65EE26538CCFE646587B5978A801" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_824359FCB00E6F755444587B5C039957" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_D8D4BDA3DF93C1218F83587CE5FDDC59" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_824359FCB00E6F755444587B5C039957" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice" xlink:label="loc_qlys_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice_4FFD1F052217DC519921587BA712742D" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_87C27276D4278F38DFA5587A25E5AB71" xlink:to="loc_qlys_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice_4FFD1F052217DC519921587BA712742D" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.qualys.com/role/EmployeeStockAndBenefitPlansStockOptionActivityDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.qualys.com/role/EmployeeStockAndBenefitPlansTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.qualys.com/role/FairValueOfFinancialInstruments" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.qualys.com/role/FairValueOfFinancialInstrumentsCashAndCashEquivalentsAvailableForSaleSecuritiesRestrictedCashReconciliationDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems" xlink:label="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_AE8C9DFD9B653B14E0794A7B85DA3906" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_FairValueByBalanceSheetGroupingTable" xlink:label="loc_us-gaap_FairValueByBalanceSheetGroupingTable_1F30DB9A685B97259D404A7B85D8F045" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_AE8C9DFD9B653B14E0794A7B85DA3906" xlink:to="loc_us-gaap_FairValueByBalanceSheetGroupingTable_1F30DB9A685B97259D404A7B85D8F045" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_BalanceSheetLocationAxis" xlink:label="loc_us-gaap_BalanceSheetLocationAxis_CC0ABB1FE6EAE38F4BAF4A7B85D81959" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_1F30DB9A685B97259D404A7B85D8F045" xlink:to="loc_us-gaap_BalanceSheetLocationAxis_CC0ABB1FE6EAE38F4BAF4A7B85D81959" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_BalanceSheetLocationDomain" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_CDAB12D9043776206AA14A7B85D86275_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_CC0ABB1FE6EAE38F4BAF4A7B85D81959" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_CDAB12D9043776206AA14A7B85D86275_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_BalanceSheetLocationDomain" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_CDAB12D9043776206AA14A7B85D86275" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_CC0ABB1FE6EAE38F4BAF4A7B85D81959" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_CDAB12D9043776206AA14A7B85D86275" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_CashAndCashEquivalentsMember" xlink:label="loc_us-gaap_CashAndCashEquivalentsMember_F59517BAD999C8CAE16B4A7B85D8E8AB" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_CDAB12D9043776206AA14A7B85D86275" xlink:to="loc_us-gaap_CashAndCashEquivalentsMember_F59517BAD999C8CAE16B4A7B85D8E8AB" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_AvailableForSaleSecuritiesLineItemMember" xlink:label="loc_qlys_AvailableForSaleSecuritiesLineItemMember_14ED04B5AEAF5A9974524A7B85D84322" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_CDAB12D9043776206AA14A7B85D86275" xlink:to="loc_qlys_AvailableForSaleSecuritiesLineItemMember_14ED04B5AEAF5A9974524A7B85D84322" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_LongTermInvestmentsMember" xlink:label="loc_qlys_LongTermInvestmentsMember_3D3BED173F3BC054FB954A7B85D93E35" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_CDAB12D9043776206AA14A7B85D86275" xlink:to="loc_qlys_LongTermInvestmentsMember_3D3BED173F3BC054FB954A7B85D93E35" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_F2F04A83DDACC1C64BB84A7B85D97138" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_1F30DB9A685B97259D404A7B85D8F045" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_F2F04A83DDACC1C64BB84A7B85D97138" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_46AC0A23C47AE8DB9A114A7B85D9371F_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_F2F04A83DDACC1C64BB84A7B85D97138" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_46AC0A23C47AE8DB9A114A7B85D9371F_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_46AC0A23C47AE8DB9A114A7B85D9371F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_F2F04A83DDACC1C64BB84A7B85D97138" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_46AC0A23C47AE8DB9A114A7B85D9371F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_CashMember" xlink:label="loc_us-gaap_CashMember_40DE836AA1F8C4D4D5F44A7B85D977D5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_46AC0A23C47AE8DB9A114A7B85D9371F" xlink:to="loc_us-gaap_CashMember_40DE836AA1F8C4D4D5F44A7B85D977D5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_MoneyMarketFundsMember" xlink:label="loc_us-gaap_MoneyMarketFundsMember_368E073A29E6661EC58A4A7B85D95E18" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_46AC0A23C47AE8DB9A114A7B85D9371F" xlink:to="loc_us-gaap_MoneyMarketFundsMember_368E073A29E6661EC58A4A7B85D95E18" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_USGovernmentAgenciesDebtSecuritiesMember" xlink:label="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_6DEFD82FCA01553C2E754A7B85DA8623" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_46AC0A23C47AE8DB9A114A7B85D9371F" xlink:to="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_6DEFD82FCA01553C2E754A7B85DA8623" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_CommercialPaperMember" xlink:label="loc_us-gaap_CommercialPaperMember_C8C8A4AAA97F83F8539E4A7B85DAEEE9" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_46AC0A23C47AE8DB9A114A7B85D9371F" xlink:to="loc_us-gaap_CommercialPaperMember_C8C8A4AAA97F83F8539E4A7B85DAEEE9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_CorporateBondSecuritiesMember" xlink:label="loc_us-gaap_CorporateBondSecuritiesMember_B8AE062DACA87E670BC64A7B85DA60EA" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_46AC0A23C47AE8DB9A114A7B85D9371F" xlink:to="loc_us-gaap_CorporateBondSecuritiesMember_B8AE062DACA87E670BC64A7B85DA60EA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AssetBackedSecuritiesMember" xlink:label="loc_us-gaap_AssetBackedSecuritiesMember_1F6F609891CF12257B7D4A7B85DA41A2" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_46AC0A23C47AE8DB9A114A7B85D9371F" xlink:to="loc_us-gaap_AssetBackedSecuritiesMember_1F6F609891CF12257B7D4A7B85DA41A2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract" xlink:label="loc_us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract_FFA188FAB89E32ACE2F34A7B85DACDA3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_AE8C9DFD9B653B14E0794A7B85DA3906" xlink:to="loc_us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract_FFA188FAB89E32ACE2F34A7B85DACDA3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AvailableForSaleSecuritiesAmortizedCost" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesAmortizedCost_CBA22AF673AA9A28A0D04A7B85DB97F6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract_FFA188FAB89E32ACE2F34A7B85DACDA3" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesAmortizedCost_CBA22AF673AA9A28A0D04A7B85DB97F6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_805E1C0EA4BA32B0C9494A7B85DB2B85" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract_FFA188FAB89E32ACE2F34A7B85DACDA3" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_805E1C0EA4BA32B0C9494A7B85DB2B85" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_AA8968ADE61972058FE24A7B85DB44EF" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract_FFA188FAB89E32ACE2F34A7B85DACDA3" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_AA8968ADE61972058FE24A7B85DB44EF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AvailableForSaleSecuritiesCurrent" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesCurrent_0C77ADD08CF8F33A6A064A7B85DBF137" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialInstrumentsFinancialAssetsBalanceSheetGroupingsAbstract_FFA188FAB89E32ACE2F34A7B85DACDA3" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesCurrent_0C77ADD08CF8F33A6A064A7B85DBF137" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.qualys.com/role/FairValueOfFinancialInstrumentsContractualMaturityDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems" xlink:label="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_A0A8B46E9DBB8069902E4A7B85984C0C" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesTable" xlink:label="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesTable_8AD503A12DE5ED71940A4A7B859797F0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_A0A8B46E9DBB8069902E4A7B85984C0C" xlink:to="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesTable_8AD503A12DE5ED71940A4A7B859797F0" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_C25F16A0A600A0B102DC4A7B8597E536" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesTable_8AD503A12DE5ED71940A4A7B859797F0" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_C25F16A0A600A0B102DC4A7B8597E536" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_FFD9C918ED37398CF76F4A7B85974413_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_C25F16A0A600A0B102DC4A7B8597E536" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_FFD9C918ED37398CF76F4A7B85974413_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_FFD9C918ED37398CF76F4A7B85974413" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_C25F16A0A600A0B102DC4A7B8597E536" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_FFD9C918ED37398CF76F4A7B85974413" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_CommercialPaperMember" xlink:label="loc_us-gaap_CommercialPaperMember_D8A333450F2A2C390D5C4A7B85982E28" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_FFD9C918ED37398CF76F4A7B85974413" xlink:to="loc_us-gaap_CommercialPaperMember_D8A333450F2A2C390D5C4A7B85982E28" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_USGovernmentAgenciesDebtSecuritiesMember" xlink:label="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_1A15087EBD3267BF6F3E4A7B85983693" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_FFD9C918ED37398CF76F4A7B85974413" xlink:to="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_1A15087EBD3267BF6F3E4A7B85983693" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_CorporateBondSecuritiesMember" xlink:label="loc_us-gaap_CorporateBondSecuritiesMember_5876BAC77AA6DBC13B474A7B859843E8" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_FFD9C918ED37398CF76F4A7B85974413" xlink:to="loc_us-gaap_CorporateBondSecuritiesMember_5876BAC77AA6DBC13B474A7B859843E8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AssetBackedSecuritiesMember" xlink:label="loc_us-gaap_AssetBackedSecuritiesMember_9366470C3F36365323614A7B8598A1B2" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_FFD9C918ED37398CF76F4A7B85974413" xlink:to="loc_us-gaap_AssetBackedSecuritiesMember_9366470C3F36365323614A7B8598A1B2" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_AvailableForSaleSecuritiesDebtAndEquityMaturitiesNextTwelveMonthsFairValue" xlink:label="loc_qlys_AvailableForSaleSecuritiesDebtAndEquityMaturitiesNextTwelveMonthsFairValue_B5D5DECBC8A5E05689814A7B8598E539" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_A0A8B46E9DBB8069902E4A7B85984C0C" xlink:to="loc_qlys_AvailableForSaleSecuritiesDebtAndEquityMaturitiesNextTwelveMonthsFairValue_B5D5DECBC8A5E05689814A7B8598E539" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_AvailableForSaleSecuritiesDebtAndEquityMaturitiesYearOneThroughTwoFairValue" xlink:label="loc_qlys_AvailableForSaleSecuritiesDebtAndEquityMaturitiesYearOneThroughTwoFairValue_0701524936C626B3E4D74A7B8599C3BB" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_A0A8B46E9DBB8069902E4A7B85984C0C" xlink:to="loc_qlys_AvailableForSaleSecuritiesDebtAndEquityMaturitiesYearOneThroughTwoFairValue_0701524936C626B3E4D74A7B8599C3BB" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_AvailableForSaleSecuritiesDebtAndEquityMaturitiesAfterYearTwoFairValue" xlink:label="loc_qlys_AvailableForSaleSecuritiesDebtAndEquityMaturitiesAfterYearTwoFairValue_CF320CA329E3026453774A7B859909B5" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_A0A8B46E9DBB8069902E4A7B85984C0C" xlink:to="loc_qlys_AvailableForSaleSecuritiesDebtAndEquityMaturitiesAfterYearTwoFairValue_CF320CA329E3026453774A7B859909B5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AvailableForSaleSecurities" xlink:label="loc_us-gaap_AvailableForSaleSecurities_64FDA64B76EFD918221C4A7B85990997" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_A0A8B46E9DBB8069902E4A7B85984C0C" xlink:to="loc_us-gaap_AvailableForSaleSecurities_64FDA64B76EFD918221C4A7B85990997" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.qualys.com/role/FairValueOfFinancialInstrumentsFairValueHierarchyDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_15C7A5D17580CB13DD7B4A7B85BC5167" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_CD5EAF4BE6F7B83FB4824A7B85B45575" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_15C7A5D17580CB13DD7B4A7B85BC5167" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_CD5EAF4BE6F7B83FB4824A7B85B45575" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_DerivativeByNatureAxis" xlink:label="loc_us-gaap_DerivativeByNatureAxis_ED5A50D6A746F7BF6CD84A7B85B4934E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_CD5EAF4BE6F7B83FB4824A7B85B45575" xlink:to="loc_us-gaap_DerivativeByNatureAxis_ED5A50D6A746F7BF6CD84A7B85B4934E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_DerivativeNameDomain" xlink:label="loc_us-gaap_DerivativeNameDomain_E93C7B3630FFF6CBC28F4A7B85B4E889_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeByNatureAxis_ED5A50D6A746F7BF6CD84A7B85B4934E" xlink:to="loc_us-gaap_DerivativeNameDomain_E93C7B3630FFF6CBC28F4A7B85B4E889_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_DerivativeNameDomain" xlink:label="loc_us-gaap_DerivativeNameDomain_E93C7B3630FFF6CBC28F4A7B85B4E889" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeByNatureAxis_ED5A50D6A746F7BF6CD84A7B85B4934E" xlink:to="loc_us-gaap_DerivativeNameDomain_E93C7B3630FFF6CBC28F4A7B85B4E889" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ForwardContractsMember" xlink:label="loc_us-gaap_ForwardContractsMember_81B775B5740B7FF4915A4A7B85B4B527" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeNameDomain_E93C7B3630FFF6CBC28F4A7B85B4E889" xlink:to="loc_us-gaap_ForwardContractsMember_81B775B5740B7FF4915A4A7B85B4B527" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_1FB79B2DAB9B0258C4E34A7B85B4CACE" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_CD5EAF4BE6F7B83FB4824A7B85B45575" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_1FB79B2DAB9B0258C4E34A7B85B4CACE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_075058509E5A94A5DDE24A7B85B4E79C_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_1FB79B2DAB9B0258C4E34A7B85B4CACE" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_075058509E5A94A5DDE24A7B85B4E79C_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_075058509E5A94A5DDE24A7B85B4E79C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_1FB79B2DAB9B0258C4E34A7B85B4CACE" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_075058509E5A94A5DDE24A7B85B4E79C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_CommercialPaperMember" xlink:label="loc_us-gaap_CommercialPaperMember_3771D1B82C93B4D415F74A7B85B52AF7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_075058509E5A94A5DDE24A7B85B4E79C" xlink:to="loc_us-gaap_CommercialPaperMember_3771D1B82C93B4D415F74A7B85B52AF7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_USGovernmentAgenciesDebtSecuritiesMember" xlink:label="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_51AB8997F5B93B491E2B4A7B85B552DE" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_075058509E5A94A5DDE24A7B85B4E79C" xlink:to="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_51AB8997F5B93B491E2B4A7B85B552DE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_CorporateBondSecuritiesMember" xlink:label="loc_us-gaap_CorporateBondSecuritiesMember_570F19C2339DAEAD04B94A7B85B54C14" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_075058509E5A94A5DDE24A7B85B4E79C" xlink:to="loc_us-gaap_CorporateBondSecuritiesMember_570F19C2339DAEAD04B94A7B85B54C14" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AssetBackedSecuritiesMember" xlink:label="loc_us-gaap_AssetBackedSecuritiesMember_8202C0AB6087882B703D4A7B85B55E3D" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_075058509E5A94A5DDE24A7B85B4E79C" xlink:to="loc_us-gaap_AssetBackedSecuritiesMember_8202C0AB6087882B703D4A7B85B55E3D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_5FB5BD284A7E6C114B374A7B85B50202" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_CD5EAF4BE6F7B83FB4824A7B85B45575" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_5FB5BD284A7E6C114B374A7B85B50202" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_9952214326FF2740681C4A7B85BA3293_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_5FB5BD284A7E6C114B374A7B85B50202" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_9952214326FF2740681C4A7B85BA3293_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_9952214326FF2740681C4A7B85BA3293" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_5FB5BD284A7E6C114B374A7B85B50202" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_9952214326FF2740681C4A7B85BA3293" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_FairValueInputsLevel1Member" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_F7E88218682AF6BEFA634A7B85BA3CE9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_9952214326FF2740681C4A7B85BA3293" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_F7E88218682AF6BEFA634A7B85BA3CE9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_FairValueInputsLevel2Member" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_66F7B676B20BD32D69DC4A7B85BB19F8" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_9952214326FF2740681C4A7B85BA3293" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_66F7B676B20BD32D69DC4A7B85BB19F8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_FairValueInputsLevel3Member" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_A9C6A6BC40885BD13EB34A7B85BBC74A" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_9952214326FF2740681C4A7B85BA3293" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_A9C6A6BC40885BD13EB34A7B85BBC74A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_FairValueByMeasurementFrequencyAxis" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_A8B2E98907993B687D4D4A7B85BB40B5" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_CD5EAF4BE6F7B83FB4824A7B85B45575" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_A8B2E98907993B687D4D4A7B85BB40B5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_FCA08E2EC0A87516A8094A7B85BB2ADD_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_A8B2E98907993B687D4D4A7B85BB40B5" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_FCA08E2EC0A87516A8094A7B85BB2ADD_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_FCA08E2EC0A87516A8094A7B85BB2ADD" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_A8B2E98907993B687D4D4A7B85BB40B5" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_FCA08E2EC0A87516A8094A7B85BB2ADD" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_FairValueMeasurementsRecurringMember" xlink:label="loc_us-gaap_FairValueMeasurementsRecurringMember_C47C93A51F42A0382A754A7B85BB591F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_FCA08E2EC0A87516A8094A7B85BB2ADD" xlink:to="loc_us-gaap_FairValueMeasurementsRecurringMember_C47C93A51F42A0382A754A7B85BB591F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_FairValueByMeasurementBasisAxis" xlink:label="loc_us-gaap_FairValueByMeasurementBasisAxis_F1CB02E986D0CF1180104A7B85BB9BEA" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_CD5EAF4BE6F7B83FB4824A7B85B45575" xlink:to="loc_us-gaap_FairValueByMeasurementBasisAxis_F1CB02E986D0CF1180104A7B85BB9BEA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_29BF3C1726ABBEA310D24A7B85BC8F13_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_F1CB02E986D0CF1180104A7B85BB9BEA" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_29BF3C1726ABBEA310D24A7B85BC8F13_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_FairValueDisclosureItemAmountsDomain" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_BDFBBC1E3B80484647DB4A7B85BB7576" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_F1CB02E986D0CF1180104A7B85BB9BEA" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_BDFBBC1E3B80484647DB4A7B85BB7576" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_29BF3C1726ABBEA310D24A7B85BC8F13" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_BDFBBC1E3B80484647DB4A7B85BB7576" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_29BF3C1726ABBEA310D24A7B85BC8F13" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_758E0F8BB8D9DC5241644A7B85BC4E83" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_BDFBBC1E3B80484647DB4A7B85BB7576" xlink:to="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_758E0F8BB8D9DC5241644A7B85BC4E83" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AssetsFairValueDisclosureAbstract" xlink:label="loc_us-gaap_AssetsFairValueDisclosureAbstract_9A7496E1D6843470137D4A7B85BCB42B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_15C7A5D17580CB13DD7B4A7B85BC5167" xlink:to="loc_us-gaap_AssetsFairValueDisclosureAbstract_9A7496E1D6843470137D4A7B85BCB42B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AvailableForSaleSecurities" xlink:label="loc_us-gaap_AvailableForSaleSecurities_6D514288799ED55833E84A7B85BCE172" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_9A7496E1D6843470137D4A7B85BCB42B" xlink:to="loc_us-gaap_AvailableForSaleSecurities_6D514288799ED55833E84A7B85BCE172" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.qualys.com/role/FairValueOfFinancialInstrumentsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_2F167E0EEFFC052CAF7C4A7B8584F0D9" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_C4512C1A5C25981AB96E4A7B8583EC31" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_2F167E0EEFFC052CAF7C4A7B8584F0D9" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_C4512C1A5C25981AB96E4A7B8583EC31" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_DerivativeByNatureAxis" xlink:label="loc_us-gaap_DerivativeByNatureAxis_2964CB5BEC2C80ECEB064A7B85835BE2" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_C4512C1A5C25981AB96E4A7B8583EC31" xlink:to="loc_us-gaap_DerivativeByNatureAxis_2964CB5BEC2C80ECEB064A7B85835BE2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_DerivativeNameDomain" xlink:label="loc_us-gaap_DerivativeNameDomain_0891A64011C4663FF7F74A7B85838DF4_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeByNatureAxis_2964CB5BEC2C80ECEB064A7B85835BE2" xlink:to="loc_us-gaap_DerivativeNameDomain_0891A64011C4663FF7F74A7B85838DF4_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_DerivativeNameDomain" xlink:label="loc_us-gaap_DerivativeNameDomain_0891A64011C4663FF7F74A7B85838DF4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeByNatureAxis_2964CB5BEC2C80ECEB064A7B85835BE2" xlink:to="loc_us-gaap_DerivativeNameDomain_0891A64011C4663FF7F74A7B85838DF4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ForwardContractsMember" xlink:label="loc_us-gaap_ForwardContractsMember_E490EDB4622613E7D9E94A7B85843A27" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeNameDomain_0891A64011C4663FF7F74A7B85838DF4" xlink:to="loc_us-gaap_ForwardContractsMember_E490EDB4622613E7D9E94A7B85843A27" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ForeignCurrencyContractAssetFairValueDisclosure" xlink:label="loc_us-gaap_ForeignCurrencyContractAssetFairValueDisclosure_2E211EC06BD065590CC74A7B8584561B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_2F167E0EEFFC052CAF7C4A7B8584F0D9" xlink:to="loc_us-gaap_ForeignCurrencyContractAssetFairValueDisclosure_2E211EC06BD065590CC74A7B8584561B" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.qualys.com/role/FairValueOfFinancialInstrumentsTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.qualys.com/role/GoodwillAndIntangibleAssetsNet" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.qualys.com/role/GoodwillAndIntangibleAssetsNetDetails" xlink:type="extended">
    <link:loc xlink:href="qlys-20161231.xsd#qlys_ScheduleOfGoodwillAndIntangibleAssetsLineItems" xlink:label="loc_qlys_ScheduleOfGoodwillAndIntangibleAssetsLineItems_3C40A0FEE9B64642F36E58575A5FC215" xlink:type="locator" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_ScheduleOfGoodwillAndIntangibleAssetsTable" xlink:label="loc_qlys_ScheduleOfGoodwillAndIntangibleAssetsTable_F1234B5851D48768C3CD58575A5EAB64" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_qlys_ScheduleOfGoodwillAndIntangibleAssetsLineItems_3C40A0FEE9B64642F36E58575A5FC215" xlink:to="loc_qlys_ScheduleOfGoodwillAndIntangibleAssetsTable_F1234B5851D48768C3CD58575A5EAB64" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_F0F7A5111F9FAFC9259458575A5E897D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_qlys_ScheduleOfGoodwillAndIntangibleAssetsTable_F1234B5851D48768C3CD58575A5EAB64" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_F0F7A5111F9FAFC9259458575A5E897D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_07DE9079F01D11D659E858575A5FCD73_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_F0F7A5111F9FAFC9259458575A5E897D" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_07DE9079F01D11D659E858575A5FCD73_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_07DE9079F01D11D659E858575A5FCD73" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_F0F7A5111F9FAFC9259458575A5E897D" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_07DE9079F01D11D659E858575A5FCD73" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_DevelopedTechnologyRightsMember" xlink:label="loc_us-gaap_DevelopedTechnologyRightsMember_D84262DB70C43AE536D558575A5F489A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_07DE9079F01D11D659E858575A5FCD73" xlink:to="loc_us-gaap_DevelopedTechnologyRightsMember_D84262DB70C43AE536D558575A5F489A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_PatentsMember" xlink:label="loc_us-gaap_PatentsMember_700CBAE4A478992F5A2258575A5F1878" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_07DE9079F01D11D659E858575A5FCD73" xlink:to="loc_us-gaap_PatentsMember_700CBAE4A478992F5A2258575A5F1878" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_NonCompetitionAgreementsAndOtherIntangibleAssetsMemberMember" xlink:label="loc_qlys_NonCompetitionAgreementsAndOtherIntangibleAssetsMemberMember_71B8FBC3508DEF8A70D958575A5F2272" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_07DE9079F01D11D659E858575A5FCD73" xlink:to="loc_qlys_NonCompetitionAgreementsAndOtherIntangibleAssetsMemberMember_71B8FBC3508DEF8A70D958575A5F2272" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_D039AAFDCE873370DC3D58575A5FEF91" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_qlys_ScheduleOfGoodwillAndIntangibleAssetsLineItems_3C40A0FEE9B64642F36E58575A5FC215" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_D039AAFDCE873370DC3D58575A5FEF91" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsGross" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_B6DB205394EF46F1563458575A5F78D6" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_qlys_ScheduleOfGoodwillAndIntangibleAssetsLineItems_3C40A0FEE9B64642F36E58575A5FC215" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_B6DB205394EF46F1563458575A5F78D6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_8EDE87196D18F30FAFCE58575A5FB71C" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_qlys_ScheduleOfGoodwillAndIntangibleAssetsLineItems_3C40A0FEE9B64642F36E58575A5FC215" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_8EDE87196D18F30FAFCE58575A5FB71C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsNet" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_D5CA496B2A3A51082A5658575A5F6E37" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_qlys_ScheduleOfGoodwillAndIntangibleAssetsLineItems_3C40A0FEE9B64642F36E58575A5FC215" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_D5CA496B2A3A51082A5658575A5F6E37" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_4DC47090B3872C27D39A58575A5F06FE" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_qlys_ScheduleOfGoodwillAndIntangibleAssetsLineItems_3C40A0FEE9B64642F36E58575A5FC215" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_4DC47090B3872C27D39A58575A5F06FE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_IntangibleAssetsNetExcludingGoodwill" xlink:label="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_7F7B02839EE548045F7E58575A5FC815" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_qlys_ScheduleOfGoodwillAndIntangibleAssetsLineItems_3C40A0FEE9B64642F36E58575A5FC215" xlink:to="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_7F7B02839EE548045F7E58575A5FC815" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AmortizationOfIntangibleAssets" xlink:label="loc_us-gaap_AmortizationOfIntangibleAssets_4533D3D57FED8B65BDC158575A5F938E" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_qlys_ScheduleOfGoodwillAndIntangibleAssetsLineItems_3C40A0FEE9B64642F36E58575A5FC215" xlink:to="loc_us-gaap_AmortizationOfIntangibleAssets_4533D3D57FED8B65BDC158575A5F938E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ImpairmentOfIntangibleAssetsExcludingGoodwill" xlink:label="loc_us-gaap_ImpairmentOfIntangibleAssetsFinitelived_0759D195CCF4E36FC8E858575A5F64AF" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_qlys_ScheduleOfGoodwillAndIntangibleAssetsLineItems_3C40A0FEE9B64642F36E58575A5FC215" xlink:to="loc_us-gaap_ImpairmentOfIntangibleAssetsFinitelived_0759D195CCF4E36FC8E858575A5F64AF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_Goodwill" xlink:label="loc_us-gaap_Goodwill_308C7790C571F042848958575A5FB97B" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_qlys_ScheduleOfGoodwillAndIntangibleAssetsLineItems_3C40A0FEE9B64642F36E58575A5FC215" xlink:to="loc_us-gaap_Goodwill_308C7790C571F042848958575A5FB97B" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.qualys.com/role/GoodwillAndIntangibleAssetsNetFutureAmortizationDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.qualys.com/role/GoodwillAndIntangibleAssetsNetTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.qualys.com/role/IncomeTaxes" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.qualys.com/role/IncomeTaxesDeferredTaxAssetsAndLiabilitiesDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.qualys.com/role/IncomeTaxesIncomeBeforeProvisionForBenefitFromIncomeTaxesDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.qualys.com/role/IncomeTaxesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:href="qlys-20161231.xsd#qlys_IncomeTaxLineItems" xlink:label="loc_qlys_IncomeTaxLineItems_2736875ACE0F6DC930A761ECADDCF65C" xlink:type="locator" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_IncomeTaxTable" xlink:label="loc_qlys_IncomeTaxTable_350FD7220A8AA982D94661ECADDB9E6F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_qlys_IncomeTaxLineItems_2736875ACE0F6DC930A761ECADDCF65C" xlink:to="loc_qlys_IncomeTaxTable_350FD7220A8AA982D94661ECADDB9E6F" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_IncomeTaxAuthorityAxis" xlink:label="loc_us-gaap_IncomeTaxAuthorityAxis_539F6552B5520136AF0361ECADDB61F0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_qlys_IncomeTaxTable_350FD7220A8AA982D94661ECADDB9E6F" xlink:to="loc_us-gaap_IncomeTaxAuthorityAxis_539F6552B5520136AF0361ECADDB61F0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_IncomeTaxAuthorityDomain" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_A064199A3658455892CC61ECADDB7361_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_539F6552B5520136AF0361ECADDB61F0" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_A064199A3658455892CC61ECADDB7361_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_IncomeTaxAuthorityDomain" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_A064199A3658455892CC61ECADDB7361" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_539F6552B5520136AF0361ECADDB61F0" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_A064199A3658455892CC61ECADDB7361" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_InternalRevenueServiceIRSMember" xlink:label="loc_us-gaap_InternalRevenueServiceIRSMember_1E826155063AA1A40B3461ECADDB021F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_A064199A3658455892CC61ECADDB7361" xlink:to="loc_us-gaap_InternalRevenueServiceIRSMember_1E826155063AA1A40B3461ECADDB021F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_StateAndLocalJurisdictionMember" xlink:label="loc_us-gaap_StateAndLocalJurisdictionMember_5163C902BBC9A025125161ECADDB15F5" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_A064199A3658455892CC61ECADDB7361" xlink:to="loc_us-gaap_StateAndLocalJurisdictionMember_5163C902BBC9A025125161ECADDB15F5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_DomesticCountryMember" xlink:label="loc_us-gaap_DomesticCountryMember_6D02E13378C5D1E26A5661ECADDBC4ED" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_A064199A3658455892CC61ECADDB7361" xlink:to="loc_us-gaap_DomesticCountryMember_6D02E13378C5D1E26A5661ECADDBC4ED" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_TaxCreditCarryforwardAxis" xlink:label="loc_us-gaap_TaxCreditCarryforwardAxis_96E47A0D47B63C71333261ECADDB4196" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_qlys_IncomeTaxTable_350FD7220A8AA982D94661ECADDB9E6F" xlink:to="loc_us-gaap_TaxCreditCarryforwardAxis_96E47A0D47B63C71333261ECADDB4196" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_TaxCreditCarryforwardNameDomain" xlink:label="loc_us-gaap_TaxCreditCarryforwardNameDomain_4A1F1091837D6FE01B3161ECADDBA449_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TaxCreditCarryforwardAxis_96E47A0D47B63C71333261ECADDB4196" xlink:to="loc_us-gaap_TaxCreditCarryforwardNameDomain_4A1F1091837D6FE01B3161ECADDBA449_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_TaxCreditCarryforwardNameDomain" xlink:label="loc_us-gaap_TaxCreditCarryforwardNameDomain_4A1F1091837D6FE01B3161ECADDBA449" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TaxCreditCarryforwardAxis_96E47A0D47B63C71333261ECADDB4196" xlink:to="loc_us-gaap_TaxCreditCarryforwardNameDomain_4A1F1091837D6FE01B3161ECADDBA449" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ResearchMember" xlink:label="loc_us-gaap_ResearchMember_DE8FD8FE9C94D6399E3461ECADDC0B91" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TaxCreditCarryforwardNameDomain_4A1F1091837D6FE01B3161ECADDBA449" xlink:to="loc_us-gaap_ResearchMember_DE8FD8FE9C94D6399E3461ECADDC0B91" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_IncomeTaxExpenseBenefit" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_EFF61E3145B716FF378D61ECADDCB117" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_qlys_IncomeTaxLineItems_2736875ACE0F6DC930A761ECADDCF65C" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_EFF61E3145B716FF378D61ECADDCB117" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_DeferredTaxAssetsValuationAllowance" xlink:label="loc_us-gaap_DeferredTaxAssetsValuationAllowance_795B1C8E44A3890E4E7E61ECADDC610D" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_qlys_IncomeTaxLineItems_2736875ACE0F6DC930A761ECADDCF65C" xlink:to="loc_us-gaap_DeferredTaxAssetsValuationAllowance_795B1C8E44A3890E4E7E61ECADDC610D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount" xlink:label="loc_us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount_ED29F9AE4BF01AF09A5E61ECADDC5E79" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_qlys_IncomeTaxLineItems_2736875ACE0F6DC930A761ECADDCF65C" xlink:to="loc_us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount_ED29F9AE4BF01AF09A5E61ECADDC5E79" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_OperatingLossCarryforwards" xlink:label="loc_us-gaap_OperatingLossCarryforwards_56DCA91291F80CABD94461ECADDCFF7A" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_qlys_IncomeTaxLineItems_2736875ACE0F6DC930A761ECADDCF65C" xlink:to="loc_us-gaap_OperatingLossCarryforwards_56DCA91291F80CABD94461ECADDCFF7A" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_OperatingLossCarryforwardsExcessTaxBenefits" xlink:label="loc_qlys_OperatingLossCarryforwardsExcessTaxBenefits_7DD07442618A58194396621CC0689C65" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_qlys_IncomeTaxLineItems_2736875ACE0F6DC930A761ECADDCF65C" xlink:to="loc_qlys_OperatingLossCarryforwardsExcessTaxBenefits_7DD07442618A58194396621CC0689C65" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_TaxCreditCarryforwardAmount" xlink:label="loc_us-gaap_TaxCreditCarryforwardAmount_7FBF08B8FC441E3A92A261ECADDC3A37" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_qlys_IncomeTaxLineItems_2736875ACE0F6DC930A761ECADDCF65C" xlink:to="loc_us-gaap_TaxCreditCarryforwardAmount_7FBF08B8FC441E3A92A261ECADDC3A37" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_UndistributedEarningsOfForeignSubsidiaries" xlink:label="loc_us-gaap_UndistributedEarningsOfForeignSubsidiaries_C818A0FB6DD4A574E2C361ECADDCA77A" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_qlys_IncomeTaxLineItems_2736875ACE0F6DC930A761ECADDCF65C" xlink:to="loc_us-gaap_UndistributedEarningsOfForeignSubsidiaries_C818A0FB6DD4A574E2C361ECADDCA77A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate" xlink:label="loc_us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate_A04C01FA4585EE71342361ECADDC1CEB" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_qlys_IncomeTaxLineItems_2736875ACE0F6DC930A761ECADDCF65C" xlink:to="loc_us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate_A04C01FA4585EE71342361ECADDC1CEB" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_IncomeTaxReconciliationTaxCreditsResearch" xlink:label="loc_us-gaap_IncomeTaxReconciliationTaxCreditsResearch_3952334552C0B94E244361ECADDD5E9E" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_qlys_IncomeTaxLineItems_2736875ACE0F6DC930A761ECADDCF65C" xlink:to="loc_us-gaap_IncomeTaxReconciliationTaxCreditsResearch_3952334552C0B94E244361ECADDD5E9E" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_DeferredTaxAssetNotRecognizedNetOperatingLossCarryforwards" xlink:label="loc_qlys_DeferredTaxAssetNotRecognizedNetOperatingLossCarryforwards_716D290B43E87096C67D61ECADDD1242" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_qlys_IncomeTaxLineItems_2736875ACE0F6DC930A761ECADDCF65C" xlink:to="loc_qlys_DeferredTaxAssetNotRecognizedNetOperatingLossCarryforwards_716D290B43E87096C67D61ECADDD1242" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.qualys.com/role/IncomeTaxesProvisionForBenefitFromIncomeTaxesDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.qualys.com/role/IncomeTaxesTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.qualys.com/role/IncomeTaxesTaxRateReconciliationDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.qualys.com/role/IncomeTaxesUnrecognizedTaxBenefitsDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.qualys.com/role/NetIncomePerShareAttributableToCommonStockholders" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.qualys.com/role/NetIncomePerShareAttributableToCommonStockholdersDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_5D203AD22D94CDA0E055681E84C7274E" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_9551052649D15B8FEE7B681E84C71EBE" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_5D203AD22D94CDA0E055681E84C7274E" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_9551052649D15B8FEE7B681E84C71EBE" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_7195AAD528DFBD06A7BB681E84C7D6C0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_9551052649D15B8FEE7B681E84C71EBE" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_7195AAD528DFBD06A7BB681E84C7D6C0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AntidilutiveSecuritiesNameDomain" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_51168E3CC95FD2A7A0A2681E84C797D0_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_7195AAD528DFBD06A7BB681E84C7D6C0" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_51168E3CC95FD2A7A0A2681E84C797D0_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AntidilutiveSecuritiesNameDomain" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_51168E3CC95FD2A7A0A2681E84C797D0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_7195AAD528DFBD06A7BB681E84C7D6C0" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_51168E3CC95FD2A7A0A2681E84C797D0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="loc_us-gaap_EmployeeStockOptionMember_953C72021C9A36273078681E84C7BCE8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_51168E3CC95FD2A7A0A2681E84C797D0" xlink:to="loc_us-gaap_EmployeeStockOptionMember_953C72021C9A36273078681E84C7BCE8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_RestrictedStockUnitsRSUMember" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_C0C484625617A1BD8B60681E84C7FB55" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_51168E3CC95FD2A7A0A2681E84C797D0" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_C0C484625617A1BD8B60681E84C7FB55" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_NumeratorAbstract" xlink:label="loc_qlys_NumeratorAbstract_26024372C9C72C6AC2FC681E84C731F7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_5D203AD22D94CDA0E055681E84C7274E" xlink:to="loc_qlys_NumeratorAbstract_26024372C9C72C6AC2FC681E84C731F7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic" xlink:label="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_70018827A67677F310F9681E84C8C20B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_qlys_NumeratorAbstract_26024372C9C72C6AC2FC681E84C731F7" xlink:to="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_70018827A67677F310F9681E84C8C20B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_NetIncomeLossAvailableToCommonStockholdersDiluted" xlink:label="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersDiluted_77A156FD435522F18BF7681E84C866B7" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_qlys_NumeratorAbstract_26024372C9C72C6AC2FC681E84C731F7" xlink:to="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersDiluted_77A156FD435522F18BF7681E84C866B7" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_DenominatorAbstract" xlink:label="loc_qlys_DenominatorAbstract_8F7BC8EF09FFB77A79E8681E84C893E0" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_5D203AD22D94CDA0E055681E84C7274E" xlink:to="loc_qlys_DenominatorAbstract_8F7BC8EF09FFB77A79E8681E84C893E0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_4E12A51C9E1430F1FF21681E84C8BC56" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_qlys_DenominatorAbstract_8F7BC8EF09FFB77A79E8681E84C893E0" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_4E12A51C9E1430F1FF21681E84C8BC56" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_DilutiveSecuritiesAbstract" xlink:label="loc_us-gaap_DilutiveSecuritiesAbstract_0BDE93A43BC8CC9764A8681E84C89B72" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_qlys_DenominatorAbstract_8F7BC8EF09FFB77A79E8681E84C893E0" xlink:to="loc_us-gaap_DilutiveSecuritiesAbstract_0BDE93A43BC8CC9764A8681E84C89B72" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements" xlink:label="loc_us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements_6F512D6C55C4DA1727DD681E84C8A448" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DilutiveSecuritiesAbstract_0BDE93A43BC8CC9764A8681E84C89B72" xlink:to="loc_us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements_6F512D6C55C4DA1727DD681E84C8A448" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_IncrementalCommonSharesAttributableToCallOptionsAndWarrants" xlink:label="loc_us-gaap_IncrementalCommonSharesAttributableToCallOptionsAndWarrants_D3F1AAB520945FB95EDC681E84C8072D" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DilutiveSecuritiesAbstract_0BDE93A43BC8CC9764A8681E84C89B72" xlink:to="loc_us-gaap_IncrementalCommonSharesAttributableToCallOptionsAndWarrants_D3F1AAB520945FB95EDC681E84C8072D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_32B0E7A22A731D32BE8B681E84C92D93" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_qlys_DenominatorAbstract_8F7BC8EF09FFB77A79E8681E84C893E0" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_32B0E7A22A731D32BE8B681E84C92D93" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_EarningsPerShareBasic" xlink:label="loc_us-gaap_EarningsPerShareBasic_70C398E32543BE832D6C681E84C931C0" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_5D203AD22D94CDA0E055681E84C7274E" xlink:to="loc_us-gaap_EarningsPerShareBasic_70C398E32543BE832D6C681E84C931C0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_EarningsPerShareDiluted" xlink:label="loc_us-gaap_EarningsPerShareDiluted_8964E7478ED92B088F0F681E84C9E976" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_5D203AD22D94CDA0E055681E84C7274E" xlink:to="loc_us-gaap_EarningsPerShareDiluted_8964E7478ED92B088F0F681E84C9E976" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_AntidilutiveSecuritiesAbstract" xlink:label="loc_qlys_AntidilutiveSecuritiesAbstract_C2DFF281A6D1173CA099681E84C97078" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_5D203AD22D94CDA0E055681E84C7274E" xlink:to="loc_qlys_AntidilutiveSecuritiesAbstract_C2DFF281A6D1173CA099681E84C97078" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_524AFC9AB07E2DFE08EE681E84C926CC" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_qlys_AntidilutiveSecuritiesAbstract_C2DFF281A6D1173CA099681E84C97078" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_524AFC9AB07E2DFE08EE681E84C926CC" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.qualys.com/role/NetIncomePerShareAttributableToCommonStockholdersTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.qualys.com/role/OtherIncomeExpenseNet" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.qualys.com/role/OtherIncomeExpenseNetDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.qualys.com/role/OtherIncomeExpenseNetTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.qualys.com/role/PropertyAndEquipmentNet" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.qualys.com/role/PropertyAndEquipmentNetDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_PropertyPlantAndEquipmentLineItems" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_C6FAF1E2771A81F14B324A7B8567CD67" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_5DA7334F0B31F5A026E94A7B8560CC51" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_C6FAF1E2771A81F14B324A7B8567CD67" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_5DA7334F0B31F5A026E94A7B8560CC51" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_73D9459B7A880C7612AE4A7B856072FF" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_5DA7334F0B31F5A026E94A7B8560CC51" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_73D9459B7A880C7612AE4A7B856072FF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_C18CE84EFBF94F0D7D8B4A7B85602F0E_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_73D9459B7A880C7612AE4A7B856072FF" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_C18CE84EFBF94F0D7D8B4A7B85602F0E_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_C18CE84EFBF94F0D7D8B4A7B85602F0E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_73D9459B7A880C7612AE4A7B856072FF" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_C18CE84EFBF94F0D7D8B4A7B85602F0E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ComputerEquipmentMember" xlink:label="loc_us-gaap_ComputerEquipmentMember_A79386D82E7D5F5FF8924A7B85602868" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_C18CE84EFBF94F0D7D8B4A7B85602F0E" xlink:to="loc_us-gaap_ComputerEquipmentMember_A79386D82E7D5F5FF8924A7B85602868" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ComputerSoftwareIntangibleAssetMember" xlink:label="loc_us-gaap_ComputerSoftwareIntangibleAssetMember_F6984CD0AE7EEFF03DAB4A7B85661F60" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_C18CE84EFBF94F0D7D8B4A7B85602F0E" xlink:to="loc_us-gaap_ComputerSoftwareIntangibleAssetMember_F6984CD0AE7EEFF03DAB4A7B85661F60" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_FurnitureAndFixturesMember" xlink:label="loc_us-gaap_FurnitureAndFixturesMember_1622DCFC4B5FCBF662BA4A7B8566363C" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_C18CE84EFBF94F0D7D8B4A7B85602F0E" xlink:to="loc_us-gaap_FurnitureAndFixturesMember_1622DCFC4B5FCBF662BA4A7B8566363C" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_ScannerAppliancesMember" xlink:label="loc_qlys_ScannerAppliancesMember_526516E2D6D633188FA04A7B85675558" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_C18CE84EFBF94F0D7D8B4A7B85602F0E" xlink:to="loc_qlys_ScannerAppliancesMember_526516E2D6D633188FA04A7B85675558" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_ScannerAppliancesAndOtherComputerEquipmentSubjectToSubscriptionMember" xlink:label="loc_qlys_ScannerAppliancesAndOtherComputerEquipmentSubjectToSubscriptionMember_EA17C4A7CEDBD4E215E64A7B85673BAE" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_qlys_ScannerAppliancesMember_526516E2D6D633188FA04A7B85675558" xlink:to="loc_qlys_ScannerAppliancesAndOtherComputerEquipmentSubjectToSubscriptionMember_EA17C4A7CEDBD4E215E64A7B85673BAE" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_ScannerAppliancesAndOtherComputerEquipmentNotPlacedInServiceMember" xlink:label="loc_qlys_ScannerAppliancesAndOtherComputerEquipmentNotPlacedInServiceMember_9D80DCC0BF2742E34D014A7B8567CFF6" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_qlys_ScannerAppliancesMember_526516E2D6D633188FA04A7B85675558" xlink:to="loc_qlys_ScannerAppliancesAndOtherComputerEquipmentNotPlacedInServiceMember_9D80DCC0BF2742E34D014A7B8567CFF6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_LeaseholdImprovementsMember" xlink:label="loc_us-gaap_LeaseholdImprovementsMember_05A7E63457F237AE779C4A7B8567FBAD" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_C18CE84EFBF94F0D7D8B4A7B85602F0E" xlink:to="loc_us-gaap_LeaseholdImprovementsMember_05A7E63457F237AE779C4A7B8567FBAD" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_OtherFixedAssetsNotPlacedInServiceMember" xlink:label="loc_qlys_OtherFixedAssetsNotPlacedInServiceMember_0BED9893D26D0DAB51A64A7B8567C177" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_C18CE84EFBF94F0D7D8B4A7B85602F0E" xlink:to="loc_qlys_OtherFixedAssetsNotPlacedInServiceMember_0BED9893D26D0DAB51A64A7B8567C177" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_PropertyPlantAndEquipmentGross" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_B116401B5D997E2921DF4A7B8567466E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_C6FAF1E2771A81F14B324A7B8567CD67" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_B116401B5D997E2921DF4A7B8567466E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_51823A2BA13D79AADB704A7B85684780" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_C6FAF1E2771A81F14B324A7B8567CD67" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_51823A2BA13D79AADB704A7B85684780" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_36A6B5A389FFAED62DDD4A7B8568CE4E" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_C6FAF1E2771A81F14B324A7B8567CD67" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_36A6B5A389FFAED62DDD4A7B8568CE4E" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_DepreciationDepletionAndAmortizationExcludingIntangibleAssetAmortization" xlink:label="loc_qlys_DepreciationDepletionAndAmortizationExcludingIntangibleAssetAmortization_C8F3B8CAF08929739B644A7B8568174D" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_C6FAF1E2771A81F14B324A7B8567CD67" xlink:to="loc_qlys_DepreciationDepletionAndAmortizationExcludingIntangibleAssetAmortization_C8F3B8CAF08929739B644A7B8568174D" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.qualys.com/role/PropertyAndEquipmentNetTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.qualys.com/role/QuarterlyFinancialInformationUnaudited" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.qualys.com/role/QuarterlyFinancialInformationUnauditedDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.qualys.com/role/QuarterlyFinancialInformationUnauditedTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.qualys.com/role/ScheduleIiScheduleOfValuationAndQualifyingAccounts" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.qualys.com/role/ScheduleIiScheduleOfValuationAndQualifyingAccountsDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ValuationAndQualifyingAccountsDisclosureLineItems" xlink:label="loc_us-gaap_ValuationAndQualifyingAccountsDisclosureLineItems_2D12CE68F8B1E5A329D74A7B82FCC586" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ValuationAndQualifyingAccountsDisclosureTable" xlink:label="loc_us-gaap_ValuationAndQualifyingAccountsDisclosureTable_083B71602E1390D19C454A7B82FA3704" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ValuationAndQualifyingAccountsDisclosureLineItems_2D12CE68F8B1E5A329D74A7B82FCC586" xlink:to="loc_us-gaap_ValuationAndQualifyingAccountsDisclosureTable_083B71602E1390D19C454A7B82FA3704" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ValuationAllowancesAndReservesTypeAxis" xlink:label="loc_us-gaap_ValuationAllowancesAndReservesTypeAxis_BB60481E6D630CFA14104A7B82FB56AA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ValuationAndQualifyingAccountsDisclosureTable_083B71602E1390D19C454A7B82FA3704" xlink:to="loc_us-gaap_ValuationAllowancesAndReservesTypeAxis_BB60481E6D630CFA14104A7B82FB56AA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ValuationAllowancesAndReservesDomain" xlink:label="loc_us-gaap_ValuationAllowancesAndReservesDomain_133435DA0FC5DA3FCD7B4A7B82FBEA23_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ValuationAllowancesAndReservesTypeAxis_BB60481E6D630CFA14104A7B82FB56AA" xlink:to="loc_us-gaap_ValuationAllowancesAndReservesDomain_133435DA0FC5DA3FCD7B4A7B82FBEA23_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ValuationAllowancesAndReservesDomain" xlink:label="loc_us-gaap_ValuationAllowancesAndReservesDomain_133435DA0FC5DA3FCD7B4A7B82FBEA23" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ValuationAllowancesAndReservesTypeAxis_BB60481E6D630CFA14104A7B82FB56AA" xlink:to="loc_us-gaap_ValuationAllowancesAndReservesDomain_133435DA0FC5DA3FCD7B4A7B82FBEA23" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_AllowanceForDoubtfulAccountsMember" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsMember_B96B52BBA162FDA1DECF4A7B82FCB392" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ValuationAllowancesAndReservesDomain_133435DA0FC5DA3FCD7B4A7B82FBEA23" xlink:to="loc_us-gaap_AllowanceForDoubtfulAccountsMember_B96B52BBA162FDA1DECF4A7B82FCB392" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_MovementInValuationAllowancesAndReservesRollForward" xlink:label="loc_us-gaap_MovementInValuationAllowancesAndReservesRollForward_E568CBAB8FFA7DD1DE954A7B82FC8004" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ValuationAndQualifyingAccountsDisclosureLineItems_2D12CE68F8B1E5A329D74A7B82FCC586" xlink:to="loc_us-gaap_MovementInValuationAllowancesAndReservesRollForward_E568CBAB8FFA7DD1DE954A7B82FC8004" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ValuationAllowancesAndReservesBalance" xlink:label="loc_us-gaap_ValuationAllowancesAndReservesBalance_9BA7D9B0C3312E892CC94A7B82FC4F66" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MovementInValuationAllowancesAndReservesRollForward_E568CBAB8FFA7DD1DE954A7B82FC8004" xlink:to="loc_us-gaap_ValuationAllowancesAndReservesBalance_9BA7D9B0C3312E892CC94A7B82FC4F66" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ValuationAllowancesAndReservesChargedToCostAndExpense" xlink:label="loc_us-gaap_ValuationAllowancesAndReservesChargedToCostAndExpense_B9F5CA465150E405B97E4A7B82FC8A86" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MovementInValuationAllowancesAndReservesRollForward_E568CBAB8FFA7DD1DE954A7B82FC8004" xlink:to="loc_us-gaap_ValuationAllowancesAndReservesChargedToCostAndExpense_B9F5CA465150E405B97E4A7B82FC8A86" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ValuationAllowancesAndReservesDeductions" xlink:label="loc_us-gaap_ValuationAllowancesAndReservesDeductions_24FEAEEAF4E06FD02B014A7B82FC1FFA" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MovementInValuationAllowancesAndReservesRollForward_E568CBAB8FFA7DD1DE954A7B82FC8004" xlink:to="loc_us-gaap_ValuationAllowancesAndReservesDeductions_24FEAEEAF4E06FD02B014A7B82FC1FFA" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.qualys.com/role/SegmentInformationAndInformationAboutGeographicArea" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.qualys.com/role/SegmentInformationAndInformationAboutGeographicAreaDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_SegmentReportingInformationLineItems" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_EAA8F2F3B8CDF8A728B44A7B8337201B" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_E63EDFAC73EDF92E6C2A4A7B83378179" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_EAA8F2F3B8CDF8A728B44A7B8337201B" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_E63EDFAC73EDF92E6C2A4A7B83378179" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_StatementGeographicalAxis" xlink:label="loc_us-gaap_StatementGeographicalAxis_09679A43288BECDED0654A7B83375BF5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_E63EDFAC73EDF92E6C2A4A7B83378179" xlink:to="loc_us-gaap_StatementGeographicalAxis_09679A43288BECDED0654A7B83375BF5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_SegmentGeographicalDomain" xlink:label="loc_us-gaap_SegmentGeographicalDomain_B7E401E3D1B294F65CB84A7B833788A2_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementGeographicalAxis_09679A43288BECDED0654A7B83375BF5" xlink:to="loc_us-gaap_SegmentGeographicalDomain_B7E401E3D1B294F65CB84A7B833788A2_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_SegmentGeographicalDomain" xlink:label="loc_us-gaap_SegmentGeographicalDomain_B7E401E3D1B294F65CB84A7B833788A2" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementGeographicalAxis_09679A43288BECDED0654A7B83375BF5" xlink:to="loc_us-gaap_SegmentGeographicalDomain_B7E401E3D1B294F65CB84A7B833788A2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.sec.gov/country/2013/country-2013-01-31.xsd#country_US" xlink:label="loc_country_US_5548322ED6EE52058E3E4A7B833752D1" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentGeographicalDomain_B7E401E3D1B294F65CB84A7B833788A2" xlink:to="loc_country_US_5548322ED6EE52058E3E4A7B833752D1" xlink:type="arc" />
    <link:loc xlink:href="qlys-20161231.xsd#qlys_OtherGeographicAreasMember" xlink:label="loc_qlys_OtherGeographicAreasMember_BB7F887FF8E3E353915E4A7B8337C0D0" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentGeographicalDomain_B7E401E3D1B294F65CB84A7B833788A2" xlink:to="loc_qlys_OtherGeographicAreasMember_BB7F887FF8E3E353915E4A7B8337C0D0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_NumberOfOperatingSegments" xlink:label="loc_us-gaap_NumberOfOperatingSegments_56D21346028EA5547EFB4A7B8338D99A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_EAA8F2F3B8CDF8A728B44A7B8337201B" xlink:to="loc_us-gaap_NumberOfOperatingSegments_56D21346028EA5547EFB4A7B8338D99A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_Revenues" xlink:label="loc_us-gaap_Revenues_7EA6B9B91B776C2A93584A7B8339766E" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_EAA8F2F3B8CDF8A728B44A7B8337201B" xlink:to="loc_us-gaap_Revenues_7EA6B9B91B776C2A93584A7B8339766E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2015/elts/us-gaap-2015-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_BE7A6BE369EFCFF213B34A7B8339F86B" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_EAA8F2F3B8CDF8A728B44A7B8337201B" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_BE7A6BE369EFCFF213B34A7B8339F86B" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.qualys.com/role/SegmentInformationAndInformationAboutGeographicAreaTables" xlink:type="extended" />
</link:linkbase>
