How does the European Union affect devolution and nationalist conflict in member states? Does the EU reduce the scope of regional self-government or enhance it? Does it promote conflict or cooperation among territorial entities? These are pressing questions in Spanish politics, where devolution has been an important tool for managing nationalist disputes, and for the Basque Country, where protacted and sometimes violent nationalist conflict persists. Addressing these issues, the book explores prospects for an autonomous Basque role in EU politics; institutional arrangements for autonomous community participation in EU decision-making; Basque government alliances with other regions and the EU's surpanational bodies; EU incentives for collaboration among Basque and central state authorities; the impact of EU decisions on politically sensitive Basque competencies, and the incidence of EU issues in nationalist disputes. It also presents a new theoretical framework for analysing the impact of the EU on regional power.