This article focuses on theoretical reflections on sovereignty and constitutionalism in the context of the globalization and Europeanisation of the nation states, their politics, and legal systems. Starting from a critical assessment of the Kelsen-Schmitt polemic, the author claims that sovereignty needs to be analysed by the sociological method in order to disclose its current structural differentiation. The constitution of society may be imagined as the multitude of self-constituted and functionally differentiated social subsystems. The constitutional pluralism argument subsequently reconceptualizes sovereignty as socially differentiated and divided between specific subsystems. The EU's differentiated constitutional domain and the paradox of divided sovereignty are used as examples of profound structural and semantic changes in contemporary national and transnational societies. While the sovereign nation-state institutions have become marginalized in political structures of European societies, the self-constitutionalization of the functionally differentiated EU legal system proceeds by internalizing the concept of divided sovereignty and using it semantically as its mode of self-reference.