The process of European integration and the transfer of political authority from the national to the European level have led to the emergence of a field of EU policy making in Brussels, which attracts professionals and experts from all EU member states. This book contributes to research on the dynamics of social integration unfolding at the heart of this field. Based on in-depth interviews with officials working for the European Commission – the EU's supranational organization – the author explores the perception and negotiation of symbolic boundaries related to their diverse national and regional backgrounds. In line with their cosmopolitan attitudes and role-conception as European civil servants, Commission officials tend to de-emphasize national and regional divisions among them. Nevertheless, subtle symbolic boundaries remain in connection with their diverse organizational cultures, working language preferences, professional values and influence and career prospects. This nuanced account of patterns of social categorization and group-making in a European context will appeal to sociologists with interests in European integration and the emergence of social fields and groups beyond the nation state.