Abstract Turkey’s future with the European Union (EU) has never looked so uncertain. Turkey’s relations with the EU are at a stalemate, with accession negotiations effectively frozen. Yet, Turkey and the EU have a high degree of functional cooperation, whereby Turkey complies with the EU acquis. Turkey has opted into the EU acquis in multiple policy areas, where its voluntary compliance prior to, or as an alternative to, accession, could be conceptualized as external differentiated integration. Turkey adjusts itself to the EU rules on foreign policy, Customs Union, the Schengen regime, and development policy, to name just a few. This chapter looks at the varying degrees of Turkish compliance with the EU acquis, and proposes that Turkey will remain an integral part of European integration.