Analyzing different works and in particular Habermas' reflection on Kant, the author reconstructs, first, his approach to international law and his political and legal cosmopolitanism. Second, he presents some critical observations on Habermas' cosmopolitanism in the context of his more general discursive theory of law and state. In this perspective, he discusses the problems of peace and of the role of the United Nations, the strategy of protection of human rights, and the question of world citizenship. He argues that Habermas' cosmopolitanism is a radicalization of Kantian tradition based on a centralization of international power and a cosmopolitan law. Finally, he develops realist arguments in favour of a non-globalistic conception of international law.