This book examines lobbying in the European Union, the practices and social trajectories of interest representatives working in Brussels. Lobbying now occupies a central place in the government of the European Union and is also at the heart of European politics, as shown by the recent Qatargate scandal. The subject of lobbying has a long history in political science, and lobbying the European Union has been the subject of now classic works (Richardson and Coen, 2009; Van Schendelen, 2013; Dür and Mateo, 2016) and specialist journals (Interest Groups and Advocacy), testifying to the great success of this subject. However, most of this work have left aside the question of the professional identity, trajectories and social properties of the actors who work on a daily basis in the coproduction of European public action. Indeed, few works are devoted to analysing their concrete practices. Despite the fact that over 12,000 organisations are now on the European Transparency Register, declaring increasing annual lobbying budgets, we still know very little about those who carry out this activity.