This chapter examines the development of Bulgarian trade unions from 1997 to 2015, before and after accession to the European Union. It aims to understand how these unions, once central to the communist regime, used the resources of the European Union to redefine their role and legitimacy in the midst of ideological and organisational change. The EU was seen as a political structure that provided them with opportunities to maintain their position as actors in the political and economic arena. Methodologically, the chapter combines the analysis of trade union programmes and documents with 72 closed questionnaires, 95 semi-structured interviews and participant observation between 2009 and 2015. The main findings show that trade unions have actively and consciously used European Union resources to consolidate internally and in the political and economic sphere, setting up mechanisms to learn new bargaining codes and building institutions and their representativeness. Two main features have persisted over time: conflicts with the state over meaningful participation in social dialogue and significant use of European resources to build social dialogue institutions and maintain their role in policy-making processes.