The European Union (EU) has been building its security and defense policy since the 1990s. The evolution of the Common Security and Defence Policy (CSDP) process has affected the non-EU European NATO members‟ position in the European security architecture. The differences in the compositions of NATO and EU members have created undesired issues. As a staunch NATO member and an accession country to the EU, Turkey has also been affected by the developments in the CSDP. This article takes Turkey as a case study in analyzing the state of affairs of the involvement of non-EU European NATO members in the CSDP.