Integration and differentiation in the European Union : theory and policies Introduction The European Union as a System of Differentiated Integration PART I: THEORY Intergovernmentalism Supranationalism Constructivism PART II: POLICIES The Single Market Economic and Monetary Union Security and Defence The Area of Freedom Security and Justice Conclusions: Integration and differentiation in the European Union. Far from displaying a uniform pattern European integration varies significantly across policy areas and individual countries. Why do some policies such as the Single Market attract non EU member states while some member states choose to opt out of specific EU policies Why are some policies deeply integrated whereas others such as defence remain intergovernmental In answering these questions this innovative text provides a state of the art introduction to the study of European integration. In this updated second edition the authors introduce the most important theoretical approaches to European integration (intergovernmentalism supranationalism constructivism and postfunctionalism) and apply these to the trajectories of key EU policy areas – including the single market monetary policy foreign and security policy and justice and home affairs. Arguing that no single theory offers a completely convincing explanation of integration and differentiation in the EU the authors put forward a new analytical perspective for describing and explaining the institutions and policies of the EU and their development over time. Written by a team of prominent scholars in the field this thought provoking book provides a new synthesis of integration theory and an original way of thinking about what the EU is and how it works. Dirk Leuffen is Professor of International Politics at the Department of Politics and Public Administration University of Konstanz Germany. Berthold Rittberger is Professor of International Relations at the Geschwister Scholl Institute of Political Science University of Munich Germany. Frank Schimmelfennig is Professor of European Politics at ETH Zurich Center for Comparative and International Studies Switzerland.