There was nothing inevitable about the amazing development of international criminal law and justice institutions since the 1990s, and neither about the proliferation of international and domestic procedures to end impunity for gross human rights violations and international crimes, in particular atrocity crimes. As socio-legal researchers engaged with the processes of global lawmaking in the arena of international criminal justice, thy found "recursive" cycles of lawmaking (Halliday 2009), which involved transnational and domestic politics and actors, and were driven by mechanisms resulting from structural characteristics of the global sphere, and the very nature of international law itself The article explores this development through the lens of three "constitutional moments " and the diagnostic struggles and contestation of the legal and political concept of genocide. Finally it analyses the emerging power of international criminal law through the processes of commitment and compliance, deterrence and expressivism. In a surprising analogy to E.P. Thompson's study of lawmaking in 18th centuy Britain, the self-binding power of law emerges as a decisive factor in international criminal lawmaking.