With the end of the cold war, developments in Europe mark a historical era which require adaptation of national governments and institutions to the new environment. The removal of basic constraints of cold war years, triggered new initiatives in political and security fields by increasing the potential European role to a global level. Security and defense are the critical fields and one should consider the US and NATO presence as a sine qua non for the European Security. Throughout cold war, NATO relieved European fears and heavy burden of defense, but it also prevented the development of an autonomous European military structure. However, from 1998 on, there is a considerable shift to the ‘Europeanist’ views which was relatively weak during the cold war years. Progress in the integration process, bitter experiences in the Balkans, constituted the basic factors of this change. The US desire to reduce its burden in defense field is an additional factor to give more incentives for more autonomy in European power projection capabilities. On the other hand, the concept of an evolving ‘European Army’ or an effective military tool should not create high expectations since the process is at its very early stages and there are many problems to be solved before any expectations. Additionally, there are many variables and uncertainties in the international environment which may reverse the positive feelings of security cooperation in Europe. About the restructuring of a European Security architecture, the institutional relationships between NATO and the EU in particular, is in the process of definition. In this process, inclusion of all possible actors will reduce the challenges of an uncertain environment by providing a certain degree of flexibility. In this regard, Turkey is one of the significant actors which may have direct or indirect influence over these new formations with its membership in NATO, geographical location or with its ties in the Balkans, in the Middle East or in the Caucasus.