In order to calculate the unintended consequences of their policies, governments conduct comprehensive assessments of the impact of legislation. In doing so, they have independent expert committees monitor them on an increasingly frequent basis. However, in what ways do these committees have an influence in this respect? And what role do they play as policy advisors in terms of dismantling bureaucracy and better legislation? This book provides new insights into the history of the development of the three most experienced supervisory bodies in Europe and the reality of how they conduct themselves. Against the backdrop of various administrative cultures, the book presents the following types of supervisory committees in detail: ‘watchdog’, ‘gatekeeper’ and ‘critical friend’. Its findings intensify the political and academic debate on the performance and efficiency of supervisory bodies.