This book seeks to develop a new approach to EU legitimacy by reformulating the classical notion of constituent power for the context of European integration and challenging the conventional theoretical assumptions regarding the EU's ultimate source of authority. Markus Patberg develops and defends the idea of constituent power as a response to the frequent complaint that the EU lacks adequate popular authorisation and accountability. In so doing, he goes beyond the conventional debate about the EU's alleged democratic deficit to address the more fundamental question of the democratic legitimacy of how the EU is constituted. The result is an important and thought-provoking contribution to the literature.