The EU-NATO relationship continues to develop at a time of significant change for both organizations. Post 9/11, NATO embarked on a fundamental transformation, recasting itself as an organization with global strategic reach and interest, focused less on Europe than ever before. At the same time, the EU is also becoming a more global political actor. Consequently, there is growing evidence that over time the EU will take the primary place in providing military security in Europe. This volume combines political and legal methods to provide a comprehensive analysis of the current and likely future relationship between the EU and NATO. The work will be of interest to all those interested in the development of these two major organizations and international security more generally, whether from a political or legal perspective.