Why have referendums on European integration proliferated since the 1970s? How are referendums accommodated within member states' constitutional orders and with what impact on the European integration process? What is the likely institutional impact of referendums on the future of the European integration process? Drawing on an interdisciplinary approach, these are just some of the fundamental questions addressed in this book. The central thesis is that the EU is faced with a 'direct democratic dilemma', which is compounded by the EU's rigid constitutional structure and a growing politicisation of the referendum device on matters related to European integration. Referendums and the European Union discusses how this dilemma has emerged to impact on the course of integration and how it can be addressed.