While the new security environment necessitates an enhanced dialogue between the EU and NATO, since 2004 Turkey opposes NATO’s sharing of sensitive intelligence information with non-NATO EU members that did not sign a bilateral agreement with NATO (i.e. the Republic of Cyprus) on protecting classified information. Through its NATO membership, Turkey constitutes a veto player in the inter-institutional relations between the EU and NATO and engages in boundary-testing strategy using active diplomacy, entangling diplomacy, and issue-linkage bargaining. Turkey engages in boundary challenging through strategic noncooperation and inter-institutional balancing against the EU. The veto gives Turkey a voice against the EU and helps Turkey pursue long-term interests, such as increasing its leverage against the EU in its accession negotiations, resolving the Cyprus problem to its advantage, and getting fully integrated into the European Defence Agency (EDA). The chapter concludes that as long as the uncertainties around Turkey’s EU accession and EDA associate membership remain and the Cyprus conflict remains unresolved, Turkey will continue to challenge its boundaries against the EU.