Constitutional review has not only expanded geographically; it has also expanded in its mission and function, acquiring new subject areas and new roles and responsibilities. In examining these new roles and responsibilities, this collection reflects on constitutional review as an aspect of constitutionalism framed in the context of multilevel governance. Bringing together a number of remarkable, yet varied, contributions, it explores how institutional changes of multilevel governance have transformed the notion, shape and substance of constitutional review. To this end, four key roles, new and old, are identified: courts act as guardian of fundamental rights, they oversee the institutional balance, they provide a deliberative forum and they assume the function of a regulatory watchdog. This book explores these different roles played by national and European courts, and the challenges brought about by the involvement in multilevel networks and the shift to new concepts of governance.