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  <xs:element id="iclr_PRAHealthSciencesIncMember" abstract="true" name="PRAHealthSciencesIncMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="iclr_DebtSecuritiesAvailableForSaleCumulativeAmountAdvancedUnderSubscriptionAgreements" abstract="false" name="DebtSecuritiesAvailableForSaleCumulativeAmountAdvancedUnderSubscriptionAgreements" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
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  <xs:element id="iclr_BusinessCombinationConsiderationTransferredPaymentsToSettleDebtObligationsThatExistedPriorToAcquisitionDate" abstract="false" name="BusinessCombinationConsiderationTransferredPaymentsToSettleDebtObligationsThatExistedPriorToAcquisitionDate" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="iclr_RestOfEuropeAndOtherCountriesMember" abstract="true" name="RestOfEuropeAndOtherCountriesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
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  <xs:element id="iclr_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedCurrentOperatingLeaseLiability" abstract="false" name="BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedCurrentOperatingLeaseLiability" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
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  <xs:element id="iclr_DeferredTaxAssetsAdditionalTaxCreditCarryforwardsNotSubjectToExpiration" abstract="false" name="DeferredTaxAssetsAdditionalTaxCreditCarryforwardsNotSubjectToExpiration" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="iclr_TopClientMember" abstract="true" name="TopClientMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="iclr_ScheduleOfShareBasedCompensationRestrictedStockUnitsPerformanceStockUnitsAwardActivityTableTextBlock" abstract="false" name="ScheduleOfShareBasedCompensationRestrictedStockUnitsPerformanceStockUnitsAwardActivityTableTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:textBlockItemType"/>
  <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_InterestExpenseCreditOther" abstract="false" name="InterestExpenseCreditOther" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="iclr_ReconciliationOfProvisionOfIncomeTaxesLineItems" abstract="true" name="ReconciliationOfProvisionOfIncomeTaxesLineItems" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="iclr_ChangeinAdvancePaymentsNettedAgainstUnbilledContractsReceivablePercent" abstract="false" name="ChangeinAdvancePaymentsNettedAgainstUnbilledContractsReceivablePercent" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:percentItemType"/>
  <xs:element id="iclr_PerformanceShareUnitMember" abstract="true" name="PerformanceShareUnitMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="iclr_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentAccruedExpensesAndOtherCurrentLiabilities" abstract="false" name="BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentAccruedExpensesAndOtherCurrentLiabilities" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="iclr_OncacareMember" abstract="true" name="OncacareMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="iclr_OtherCountriesMember" abstract="true" name="OtherCountriesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="iclr_ScheduleOfUsefulLivesForPropertyPlantEquipmentTextBlock" abstract="false" name="ScheduleOfUsefulLivesForPropertyPlantEquipmentTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:textBlockItemType"/>
  <xs:element id="iclr_OperatingLossCarryforwardsUSFederal" abstract="false" name="OperatingLossCarryforwardsUSFederal" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="iclr_VariableRateComponentOneMember" abstract="true" name="VariableRateComponentOneMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="iclr_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentOperatingLeaseRightOfUseAssets" abstract="false" name="BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentOperatingLeaseRightOfUseAssets" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="iclr_OptionPlans2008Member" abstract="true" name="OptionPlans2008Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="iclr_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentUnearnedRevenue" abstract="false" name="BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentUnearnedRevenue" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="iclr_GovernmentBondsMember" abstract="true" name="GovernmentBondsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="iclr_DisclosureOfDetailedInformationAboutFinancingCostTableTextBlock" abstract="false" name="DisclosureOfDetailedInformationAboutFinancingCostTableTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:textBlockItemType"/>
  <xs:element id="iclr_DefinedBenefitPlanSchemeContributions" abstract="false" name="DefinedBenefitPlanSchemeContributions" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="iclr_ComputerEquipmentAndCapitalizedSoftwareMember" abstract="true" name="ComputerEquipmentAndCapitalizedSoftwareMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="iclr_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentNonCurrentDeferredTaxLiabilities" abstract="false" name="BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentNonCurrentDeferredTaxLiabilities" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="iclr_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentAccountsPayable" abstract="false" name="BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentAccountsPayable" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
</xs:schema>
