This book examines the relationship between theory and reform in the European Union in the light of the new Amsterdam Treaty. It draws from a rich spectrum of regional integration theory offering an account of different approaches to the politics of European constitutional reform in the late 1990s. By establishing a link between the internal and external relations of the EU, the book develops a greater understanding of the new political and institutional dynamics of the emerging European polity and the questions that further treaty reform raise for the future evolution of the regional system. In this context, the authors assess the new European security architecture, the limits and possibilities of a genuine European foreign policy, and the role of the EU in the international system.