Chapter 1 reviews past scholarly ideals and political realities of a world constitution, focusing on the Covenant of the League of Nations and the Charter of the United Nations. It sketches out the core claims of the book according to which constitutional trends in world politics must be viewed with realistic skepticism and, in that light, can be understood in terms of a process called constitutionalization. This process does not generate the unified constitutional framework typically associated with national constitutions but manifests itself as an inadvertent by–product of piecemeal international treaty making driven by proximate objectives within issue–specific domains. The chapter then presents the major themes and limitations of the contemporary “constitutionalism beyond the state” debate and establishes how a social scientific perspective can add to this legal debate. It concludes with a preview of the book, emphasizing the main theoretical insights and empirical findings.