This book examines the impact on member states of long-term foreign policy co-operation through the EU’s Common Foreign and Security Policy (CFSP). Focusing on Germany and the UK, it provides an up-to-date account of how they have navigated and responded to the demands co-operation places on all member states and how their national foreign policies and policy-making processes have changed and adapted as a consequence. As well as exploring in depth the foreign policy traditions and institutions in both states, the book also offers detailed analyses of how they addressed two major policy questions: the Iranian nuclear crisis; and the establishment and development of the European External Action Service. The book’s synthesis of country and case studies seeks to add to our understanding of the nature of inter-state co-operation in the area of foreign and security policy and what it means for the states involved.