The European Security and Defence Policy (ESDP) is a very young and innovative structure of the European Union’s Common Foreign and Security Policy (CFSP). Since its launch in 1999 at the Summit of Cologne it has developed at such an incredible pace that even Javier Solana rhapsodised about the ESDP evolving in the speed of light. Seven years later, this dynamic of integration has decelerated to normal speed and the coherency issues connected with the integration process of the European Union (EU) have also begun to affect the ESDP which is intergovernmentally organised and hence vulnerable to coherency cracks on certain topics. The Iraq crisis in 2003 was the exemplar of this fragility. The ESDP’s decisionmaking process is based on the lowest common denominator among the EU member states. If these countries cannot agree, which was the case on the Iraq problem, the ESDP becomes less important as an EU forum of CFSP on defence issues. In consideration of the intergovernmental nature of the ESDP and its unanimous decisionmaking procedure it appears that the future of the ESDP is to a large extent dependent on the co-operation and political orientation of the ESDP member countries. In particular, the big three ESDP members of the United Kingdom, France and Germany are very influential political actors within the EU framework. In the context of the ESDP these three nations lead in the possession of military and civilian capabilities and dictate the main political streams of Europeanism versus Atlanticism as well as Intergovernmentalism versus Supranationalism within ESDP. However, despite their similarities in terms of their degree of political influence, derived from their capabilities in the ESDP, they differ in their political orientation of the main political streams. For instance, the diverging views on the transatlantic relationship appeared to be the bone of contention leading to the aforementioned Iraq crisis. In view of the conflicting positions one can ask where the ESDP is to go. Will it ever become a Defence Union? Referring to the influential role of the big three and the centrality of nation-state action in ESDP this thesis attempts to give an answer to these two questions with a credible prospect of the ESDP from a nation-centred structural realist approach. Since the structural realist concept emphasises the importance of national sovereignty in high politics this thesis concludes that the notion of the ESDP to become a Defence Union is very unlikely to occur. In addition to the pessimistic neorealist/structural realist scenario, alternative scenarios, based on the holistic current situation of the ESDP, which predict a more optimistic and probably more relevant future of the ESDP are also presented.