This is a key reference text presenting the latest first-rate approaches to the study of European enlargement.Developed and significantly expanded from a special issue of the leading Journal of European Public Policy, this new volume draws on the insights from the recently emerging theoretically-informed literature on the EU's eastern enlargement and complements these studies with original articles that combine a theoretical approach with comparative analyses. These expert contributors focus on the broader theoretical debates and their implications for the enlargement of the EU, as well as placing the enlargement of the EU within the broader context of the expansion of international organisations and the study of institutions in international relations.