This book provides an up-to-date interdisciplinary assessment of the accountability of executive power in different European States and at the European Union level. From a legal perspective, it wonders to what extent the forms of responsibility and accountability of executive power have evolved in terms of legal technique or framework. From a historical perspective, it looks at the evolution of responsibility paradigms. From a political science perspective, it examines responsibility and the expectations of European democracies in terms of authority and efficiency. The volume also has a quantitative aspect identifying, gathering and analysing statistical material on responsibility and accountability in current political regimes. The book will be a valuable resource for researchers, academics, and policy-makers in constitutional law and politics, public law, comparative law, comparative politics, legal history and government.