This book fills a significant gap in recent literature on European Union politics by examining the EU’s ‘other’ eastern enlargement, completed in 2007 with the accession of Bulgaria and Romania. It focuses on both the process and the effects of the 2007 enlargement within the wider context of the post-communist countries’ accession to the EU, and, more broadly, within the context of the history of EU enlargement. The book brings together in-depth analyses of a wide range of issues, both from a comparative perspective and through single case studies. Individual contributions shed new light onto EU enlargement through a theoretical re-evaluation of the ‘strategic action’ paradigm, as well as through historical analyses of the 2007 enlargement and of its implications for future EU enlargements. Further insight into the process of EU enlargement is gained through systematic exploration of the impact of accession on policy-making and institutional structures in Bulgaria and Romania. Altogether, the contributions exemplify the multi-faceted nature of EU enlargement and accession, as well as the extent to which the process of acceding to the EU is not completed with membership, either for the EU or for the candidate countries.This book was published as a special issue of Perspectives on European Politics and Society.