The article focuses on one of the most significant conceptual reassessments that are necessary in order to adapt the idea of sovereignty to the demands of an open and democratic society in an ever more interconnected world. Indeed, if sovereigns have to reject their absolutistic claim, this implies that they will have to share power with other national as well as infra- and supranational or international instances. This means that the concept of sovereignty has to be relocated within a pluralistic – or better, post-unitary – legal system. Following this premise, the article analyses the epistemological presuppositions that stay behind the transition from the unitary conception of order to the view that also a multiplicity of orders should not be denounced as a pathology any longer, but accepted as a fact, on the one hand, and as a desirable perspective on the other. The first step of the analysis consists in introducing the fundamental elements of the unitary conception of order in both its variants: the particularistic and the holistic. In the further section, three approaches are sketched which overcome the unitary notion of order: systems theory, post-modernism, and discourse theory. Each of these epistemological approaches lays the ground for a specific notion of post-unitary legal order: the idea of the existence of a multiplicity of self-reliant, albeit not mutually indifferent, legal systems in the first case, legal pluralism in the second, and cosmopolitan constitutionalism in the third.