This book examines one of the most significant developments in European Union politics of the past decade, namely the creation of the European Security and Defence Policy (ESDP). Despite the importance of an EU-based crisis management capability for both regional and global security, little effort has been made to capture the dynamics of the ESDP's emergence in theoretical terms, nor to explain its institutional design. Based on original theoretical and empirical research, including over 25 interviews with security policy practitioners in Brussels, Berlin and Helsinki, this comprehensive study applies an historical institutionalist approach to understanding both why and how a new security and defence policy architecture based on the NATO model emerged within the EU. The book will be of interest to academics, students and policymakers in the fields of European foreign and security policy, and European and international politics more generally. Dr. Christopher Reynolds works for the Research Executive Agency in Brussels.