In May 2004, eight former communist states in Central and Eastern Europe acceded to the European Union. This new book examines the Eastern expansion of the EU through a tripartite structure, developing an empirical, conceptual and institutional analysis to provide a rounded and substantive account of EU enlargement, with new theoretical insights. The foreword is by written by Pat Cox, former president of the European Parliament. John O'Brennan also explores: why the EU decided to expand its membership what factors drove this process forward? how did the institutional environment of the EU influence enlargement outcomes? In this context he comprehensively covers the role of the European Council, Commission and Parliament. This important volume will of great interest to students and scholars of European politics and European Union studies.