In this book, readers will see historical and theoretical evaluations, security relations of states/organizations and operational cases. Shortly, we confirm liberal intergovernmentalism from theoretical assumptions that better explains the development of ESDP and its capabilities such as planning capability. The liberal intergovernmentalists explain that the converging security interests will be facilitated by continued bargaining over CFSP, because it is difficult to change member states’ security identities in the foreign policy field. We will see the reflection of liberal intergovernmentalism in the relationship between the EU and NATO. The starategic partnership is the model of NATO-EU of organizing security and defence policy within the EU. In this context, ESDP started to be active in the EU-led operations in the Western Balkans and out-of-area of the Europe. Consequently, there is an emerging division of labour devoloping between the EU and NATO in which the EU will be a soft power with using some hard security tools or military assets, and the US and NATO will be hard power as being responsible for the conduct of more robust combat missions.