This chapter explores the moral and legal dynamics and empirical connotations attached to Habermas' normative model of global constitutionalism. In particular, the chapter engages with Habermas' claim that the UN is paradigmatic of the evolution from proto-constitutional legal tenets to the constitutional authorities of a cosmopolitan legal order. Whilst acknowledging that the UN has yet to move comprehensively in a cosmopolitan direction, the chapter argues that the UN reflects the foundations of a budding global constitutional order resembling something comparable to a legally constituted community of states and their citizens. This is as a consequence of the characteristics and innovations associated with the UN Charter which, in turn, have come to constitute prima facie aspects of a global constitution. In the process, and as the chapter articulates, the UN has come to offer a potential 'stepping stone" to the establishment of a cosmopolitan legal order.