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  <xs:element id="iclr_CommitmentToAcquireLongTermInvestments" abstract="false" name="CommitmentToAcquireLongTermInvestments" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="iclr_AllowanceForDoubtfulAccountsTextBlock" abstract="false" name="AllowanceForDoubtfulAccountsTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:textBlockItemType"/>
  <xs:element id="iclr_TaxYear20332041Member" abstract="true" name="TaxYear20332041Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="iclr_The2020LegacyPRAPlanMember" abstract="true" name="The2020LegacyPRAPlanMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="iclr_AllowanceForDoubtfulAccountsForeignCurrencyTranslationAdjustments" abstract="false" name="AllowanceForDoubtfulAccountsForeignCurrencyTranslationAdjustments" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="iclr_TaxYear2023To2036Member" abstract="true" name="TaxYear2023To2036Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="iclr_AcquiredEntityMember" abstract="true" name="AcquiredEntityMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="iclr_StockRepurchaseProgramAuthorizedPercentage" abstract="false" name="StockRepurchaseProgramAuthorizedPercentage" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="iclr_AccountsReceivableCreditLossReversal" abstract="false" name="AccountsReceivableCreditLossReversal" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="iclr_BuybackProgramMember" abstract="true" name="BuybackProgramMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="iclr_RestrictedStockUnitsTwentyThirteenMember" abstract="true" name="RestrictedStockUnitsTwentyThirteenMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="iclr_VariableRateComponentOneMember" abstract="true" name="VariableRateComponentOneMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="iclr_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentOtherNonCurrentLiabilities" abstract="false" name="BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentOtherNonCurrentLiabilities" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="iclr_ReconciliationOfProvisionOfIncomeTaxesTable" abstract="true" name="ReconciliationOfProvisionOfIncomeTaxesTable" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrldt:hypercubeItem" type="xbrli:stringItemType"/>
  <xs:element id="iclr_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentAccountsReceivableAndUnbilledRevenue" abstract="false" name="BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentAccountsReceivableAndUnbilledRevenue" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="iclr_DefinedBenefitPlanBenefitObligationBenefitsPaidAndIncreaseDecreaseForBalanceTransfers" abstract="false" name="DefinedBenefitPlanBenefitObligationBenefitsPaidAndIncreaseDecreaseForBalanceTransfers" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="iclr_PaymentsForShareRepurchaseCosts" abstract="false" name="PaymentsForShareRepurchaseCosts" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="iclr_ChangeinAdvancePaymentsNettedAgainstUnbilledContractsReceivable" abstract="false" name="ChangeinAdvancePaymentsNettedAgainstUnbilledContractsReceivable" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="iclr_The2018LegacyPRAPlanMember" abstract="true" name="The2018LegacyPRAPlanMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="iclr_OtherCustomersMember" abstract="true" name="OtherCustomersMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="iclr_ConsultantsRestrictedStockUnitsTwentyNineteenMember" abstract="true" name="ConsultantsRestrictedStockUnitsTwentyNineteenMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="iclr_NumberOfLocations" abstract="false" name="NumberOfLocations" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="iclr_Range3Member" abstract="true" name="Range3Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="iclr_ContractsReceivableGross" abstract="false" name="ContractsReceivableGross" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="iclr_RestructuringReserveUtilizations" abstract="false" name="RestructuringReserveUtilizations" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="iclr_EquityMethodInvestmentDecreaseInLoanReceivable" abstract="false" name="EquityMethodInvestmentDecreaseInLoanReceivable" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="iclr_SeniorSecuredRevolvingCreditFacilityMember" abstract="true" name="SeniorSecuredRevolvingCreditFacilityMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="iclr_EmployeeStockPlanTwentyZeroEightPlanMember" abstract="true" name="EmployeeStockPlanTwentyZeroEightPlanMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="iclr_DSBiopharmaLimitedMember" abstract="true" name="DSBiopharmaLimitedMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="iclr_RedeemableNoncontrollingInterestMember" abstract="true" name="RedeemableNoncontrollingInterestMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
</xs:schema>
