The Common Security and Defence Policy (CSDP) has come a long way since its inception as the European Security and Defence Identity under NATO. Yet more than a decade after emerging as an autonomous entity, with its own capacity for civilian crisis management and military action, the European Union's CSDP is still very much a work in progress.This fully revised and updated new edition provides the most comprehensive account available of the CSDP and the debates surrounding it. Written by a leading authority in the field, the second edition draws on the author's own extensive research in the area, including hundreds of interviews with key actors, and takes account of developments since the reforms of the Lisbon Treaty. A brand new chapter assesses international relations theory and European integration theory as tools to understand the CSDP, and critically engages with theoretical approaches that view security and defence policy as the exclusive domain of sovereign nation-states. The book concludes with an analysis of future hurdles for the European Union as it responds to new and often unpredictable crises across the globe.