Dualism and monism are two grand theories aiming at providing a theoretical basis for the problem of the effectiveness of international law. By both adopting the domestic law point of view, neither doctrine allows us to grasp the current nature of the international legal order in general and of European law in particular. In this context, the chapter examines whether the seemingly antagonistic discourse of constitutional pluralism is apt to describe current legal trends. It will notably be argued that this discourse constitutes an update of dualism and monism. While the purely constitutionalist discourse insists on unity, the doctrines of constitutional pluralism seem to be able to explain the problems connected with the intermingling of legal orders in Europe by guaranteeing, through a constitutional framework, a certain unity in diversity.