This book explores law-making in international affairs and is compiled to celebrate the fiftieth birthday of Professor Jan Klabbers, a leading international law and international relations scholar, who has made significant contributions to the understanding of the sources of international legal obligations and the idea of constitutionalism in international law. Inspired by Professor Klabbers’ wide-ranging interests in international law and his interdisciplinary approach, the book examines law-making through a variety of perspectives and seeks to break new ground in exploring what it means to think and write about law and its creation. While examining the substance of international law, these contributors raise more general concerns, such as the relationship between law-making and the application of law, the role and conflict between various institutions and the characteristics of the formal sources of international law. The book will be of great interest to students and academics of legal theory, international relations and international law.