This volume offers new practical and theoretical perspectives on one of the most complex questions regarding the formation of international law, namely that actors other than states contribute to the making of customary international law.Notwithstanding the International Law Commissions valuable contribution, the making of customary international law remains riddled with acute practical and theoretical controversies that continue to be intensively debated. Making extensive reference to the case-law of international law courts and tribunals, as well as the most recent scholarly work on customary international law, this volume provides a comprehensive study of the contribution of international organisations and non-state actors to the formation of customary international law. With innovative tools and guidance for law students, legal scholars, and researchers in law, as well as legal practitioners, advisers, judges, arbitrators, and counsels, this collection is essential reading for those wishing to understand and address contemporary questions of international law-making.

Sufyan Droubi is a Lecturer in International Law at the University of Dundee Jean dAspremont is Professor of International Law at Sciences Po Paris and the University of Manchester

Introduction: Stories about International Organisations, Non-State Actors and the Formation of Customary International Law Sufyan Droubi and Jean dAspremont 1 International Organisations as Autonomous Actors Nikolaos Voulgaris 2 Capturing the Juridical Will Catherine Brölmann 3 Opinio Juris: Between Mental States and Institutional Objects Sufyan Droubi 4 Beyond the Either-Or Paradigm Lorenzo Gasbarri 5 Between Anthropomorphism and Artificial Unity Maiko Meguro 6 Custom as the product of successful argumentative campaigns Fabian Cardenas 7 Unlearning some common tropes Jean dAspremont 8 International Organizations and non-State actors in the International Law Commissions Conclusions on Identification of Customary International law Michael Wood 9 The International Law Commission Perspective on Non-State Actors and Customary International Law Veronika Bílková 10 The International Law Commission in the Eyes of the International Law Commission: Mirror or Looking-glass? Luíza Leão Soares Pereira 11 The Riddle of Custom: General Assembly Resolutions Rossana Deplano 12 The United Nations Secretariat and Custom Jean-Baptiste Merlin 13 The Making of Custom through Sanctions of International Organisations Maru¨a T. Veber 14 The International Committee of the Red Cross and Custom Iris Müller 15 Treaty Bodies and States: Shaping Custom Kasey McCall-Smith 16 The Contribution to Customary International Law by Territories under International Administration William Thomas Worster 17 The formation of customary international law by de facto regimes Antal Berkes 18 Investors in the Formation of Customary International Law Tomoko Yamashita 19 Adjudicators, Guardians, and Enforcers: Taking the Role of Non-Governmental Organisations in Customary International Law-Making Seriously Valentina Azarova Index