Constitutional issues have topped a challenging agenda for the European Union at the start of the twenty-first century, intertwining with other issues to generate both high aspirations and serious setbacks and even, on occasion, a sense of crisis for the European project. In this important new text, Thomas Christiansen and Christine Reh look behind the headlines to provide an in-depth and systematic account of the formal and informal dynamics of constitution building in Europe. They introduce the various actors involved in the process, examine the structural opportunities and constraints on constitutional choice, and take the reader through the different stages of EU treaty reform from agenda-setting to ratification. Having charted the trajectory of constitutionalization in the EU, the authors conclude with a discussion of recent developments and future prospects. Thomas Christiansen is Professor of European Institutional Politics at Maastricht University and also holds a position as Associate Professor at the European Institute of Public Administration in Maastricht. He is co-editor of the Journal of European Integration and has published widely on EU politics. Christine Reh is Lecturer in European Politics at University MA26 London and has published works on the European Convention, integration theory and international negotiation.