International law is increasingly seen as undergoing a process of constitutionalization that rests on a Kantian understanding of law. This movement towards constitutionalization owes much to Habermas’ claim that the concept of constitution is not dependant on the concept of State, paving the way for global “governance without government” that “derives” democratic legitimacy from national arenas (Habermas, 2006). I this essay, I raise the following questions: 1) how should the concept of “universal law” be understood in Kant and Habermas’s thinking? ; 2) is this concept useful to understand contemporary international law? After a brief overview of contemporary theories on the constitutionalization of international law, I begin by presenting Kantian universalism as a philosophical principle, on the one hand, and a political project, on the other. I then question both the limits of a moral approach to international law, and the democratic legitimacy of a constitutional order without a State.
