This landmark study explores the increasingly important role that referendums play in the process of European integration. Employing an original research design, Simon Hug effectively blends formal modeling and statistical analysis to assess the consequences of European Union-wide referendums. He shows that their use has created more difficulties than the backers of direct democracy anticipated. With its detailed empirical analysis, this book makes an important contribution both to the study of referendums and to our understanding of institutional reform and integration within the EU.