The book examines how multiple and conflicting justice claims shape international negotiations. It conceptualizes justice as ambivalent, showing that efforts to promote fairness can also produce injustice. Theoretically, it traces human rights and state sovereignty to natural law traditions and introduces the concepts of a 'justice motive' and 'justization' to explain how states frame issues in moral terms. Empirically, it analyzes UN negotiations, including the Arms Trade Treaty and the UNPoA, as well as the International Criminal Court and conflict-related sexual violence. These cases show that justice claims can both enable cooperation and hinder agreements, making justice a central yet contested force in global governance.