The article presents an overview of the recent institutionalisation in Italy of the "Metropolitan cities" as introduced by the Law 56/2014. The study analyses the process of institutionalization of this new level of government, the rationales of the reform promoted by the Law and the reasons for its success in making the Metropolitan cities effective. Problematic issues that the reform has not solved and that can weaken its effectiveness are also examined, underpinning specifically the question of the boundaries and the inner spatial organization of Metropolitan cities, and the rescaling of functions from Regions and Municipalities to Metropolitan cities.