This book provides a comprehensive understanding of how, and under which conditions, regulators in the social sectors are able to influence political agendas and issue definitions. In these political processes, agencies may become the policy entrepreneurs which are able to prioritize issues, placing them in the political agenda and influencing policy formulations. These activities generate additional questions about the political role of regulatory agencies and post-delegation settings. Based on original source data and a mixed methods approach, the book shows that the diffusion of regulatory agencies is not only limited to regulatory responsibilities and to their increasing role in policy-making, but their influence has stretched over the agenda-setting phase but only under certain conditions. Moreover, the evolution of their strategies, the production and use of knowledge and the context in which they operate enable them to exert leverage on agendas. This book will be of key interest to scholars, students and practitioners of the politics of regulation, bureaucracy, agenda-setting, public policy, social problems and more broadly to European and comparative politics, and democracy.