A commonplace misconception identifies Kelsen as a one-dimensional legal positivist and Habermas as a one-dimensional legal moralist. I argue, on the contrary, that both theorists defend a complex normative conception of democratic proceduralism that straddles the positivism/naturalism divide. I then show how their extension of this conception to international law commits them to a monistic human rights regime. I conclude that their realistic acknowledgment of the fragmented nature of legal paradigms and regimes entails a complementary qualification of their monism. Section 10.1 situates Kelsen and Habermas’s proceduralism between natural law reasoning and formal positivism in opposition to Schmitt’s political-theological defense of decisionism. Section 10.2 compares the different methods by which Kelsen and Habermas defend democratic proceduralism. Section 10.3 shows how they extend this conception to international law in defending a monistic human rights regime. Section 10.4 discusses their respective views about the decisive role played by courts and constitutional review in this regime, and critically examines their proceduralist understanding of constitutional review. Section 10.5 concludes with an assessment of the limits and possibilities of constitutionalizing humanitarian law in international law in the face of persistent legal pluralization.