Europe has been surrendered by instable regions. Improving its defense capabilities and crisis management functions within the ESDP, the EU‟s chances will enhance on the world scene. In this article, the current capacity of the European security architecture and Turkey‟s position is analyzed. EU countries claim that NATO must remain for collective defense, but responsibility for crisis management and peace support operations must be shouldered by the EU. In this case, NATO may turn into a marginal organization, like the WEU in 1954, if it does not update its missions and responsibilities. The article explores the development of the European security architecture and Turkey‟s position within it. Turkey has sought to find ways to cooperate on NATO-EU cooperation under ESDP; however the EU did not fulfill its promises which led to the withdrawal of Turkey‟s military support to the EU in 2007. In addition, Turkey strongly objected Greek Cypriot government‟s co-operation with NATO and its participation in the EU's ESDP which was blocked by the NATO-EU Security Agreement