Presenting the first analytical overview of the legal foundations of the EU's Common Security and Defence Policy (CSDP), this book provides a detailed examination of the law and practice of the EU's security policy. The European Union's security and defence policy has long been the focus of political scientists and international relations experts. However, it has more recently become of increasing relevance to lawyers too. Since the early 2000s, the EU has carried out more than two dozen security and defence missions in Europe, Africa, and Asia. The EU institutions are keen to stress the security dimension of other external policies also, such as development cooperation, and the Lisbon Treaty introduces a more detailed set of rules and procedures which govern the CSDP. This book provides a legal analysis of the Union's CSDP by examining the nexus of its substantive, institutional, and economic dimensions. Taking as its starting point the historical development of security and defence in the context of European integration, it outlines the legal framework created by the rules and procedures introduced by the Treaty of Lisbon. It examines the military operations and civilian missions undertaken by the Union, and looks at the policy context within which they are carried out. It analyses the international agreements concluded in this field and explores the links between the CSDP and other external policies of the Union.