Revisiting Customary Humanitarian Law: The ICRC’s Study at 20
The Institute for International Peace and Security Law (Universität zu Köln) and the Institute for International Law of Peace and Armed Conflict (Ruhr-Universität Bochum) are hosting a workshop for young researchers, scheduled to take place in Bochum on September 18-19th, 2025. Over the course of the workshop, early career scholars will explore customary international humanitarian law in light of the ICRC’s 2005 study on this subject. We aim to gather unique perspectives from an international audience and to publish the contributions in a special volume of the Cologne Studies of International Peace and Security Law. On the twentieth anniversary of the ICRC’s Study, we hope to reinvigorate the conversation about this influential body of research.
Customary international law is one of the main sources of public international law and is recognized to bind all States. As enshrined in Article 38 (1) (b) of the Statute of the International Court of Justice, custom manifests in “a general practice accepted as law”. Yet, the identification of customary international law is not only theoretically controversial, it is also notoriously difficult to detect specific rules that have achieved customary status in practice.
Custom is of particular relevance for international humanitarian law. Since some of the key treaties comprising the law of armed conflict have not (yet) been ratified universally, in many instances the binding rules regulating conduct in war are overwhelmingly derived from customary standards. However, it is precisely in this field that custom could prove especially controversial, both because of the realities of armed conflict and considering the different interpretive communities that engage with IHL and their different emphases.
Military commanders, international bodies, and members of civil society therefore stand to benefit immensely from a clear articulation of the rules of IHL which have attained customary status. Hence, when the ICRC published its Study of Customary International Humanitarian Law in 2005 with 161 distinct rules, it attracted significant attention. Though it quickly became an authoritative source to turn to for evidence of custom, the Study remains controversial, both in terms of its contents and its methods. It may not be without shortcomings or potential for improvement, expansion, refinement, or interpretation. As is stated on the ICRC’s website itself, “While comprehensive, the study does not purport to be an exhaustive assessment of customary IHL.” We aim to provide a scholarly forum for debate as to the future of the Study and, more generally, of customary international humanitarian law.
The workshop is made possible by generous funding provided by the German Foundation for Peace Research.
More information will be made available here soon.