Winer, Customary International Law, Chap. 8, in International Law Legal Research, suggests this research strategy: (1) look in books, articles and cases on your issue to see if they identify those few treaties, General Assembly resolutions and judicial decisions that are considered to be direct statements of customary law; and (2) look in the following: books, articles, Restatement 3d Foreign Relations of the U.S., and International Law Commission materials: Identification of customary international law, draft agreements, principles and articles and the Analytical Guide to the Work of the International Law Commission, for statements of what the author thinks are the customary rules on an issue.
(3) If you have not found statements of what is customary law on your issue, then continue your research by looking for sources that provide evidence of state practice, opinio juris, jus cogens, and any other related factors. This tab lists sources for the practice of international law by other states and for U.S. practice of international law. See also Humanitarian law/Law of war.
Use the other tabs of this research guide to locate any specific sources that you need, e.g., treaties, case law, etc.
The following guides also suggest strategies and specific sources for researching customary international law.
- Researching Customary International Law, LawPORT tutorial, Institute of Advanced Legal Studies, School of Advanced Study, Univ. of London
- Customary International Law, Generally Recognized Principles, and Judicial Decisions, Chap. 7, in International and Foreign Legal Research: A Coursebook 2d ed.
By Marci Hoffman & Mary Rumsey.
- Customary International Law, Chap. 8, in International Law Legal Research
By Anthony S. Winer, Mary Ann E. Archer & Lyonette Louis-Jacques. The bibliography, pp. 208-209, lists other general books and articles on customary international law.
- Customary International Law, CALI Lesson
By Lee Peoples.
- Researching Foreign Customary Law, CALI Lesson
By Susan Gaultier.
- UPDATE: Researching Customary International Law, State Practice and the Pronouncements of States Regarding International Law, Columbia Law Library Website
Updated by Catherine Deane, originally written by Silke Sahl.
- Sources of State Practice in International Law, Brill Online
By Ralph Gaebler & Alison Shea.
- Sources of State Practice in International Law
By Ralph Gaebler & Maria Smolka-Day.
- Researching Public International Law, ASIL eRG Electronic Resources Guide
By Kelly Vinopal. See § III.B.
- National Treaty Law and Practice
Published by the American Society of International Law. Search this title in Julius to find volumes covering various countries.
- Conducting Research in Contemporary International Law, Chap. 4 in Contemporary Practice of Public International Law
By Ralph Gaebler.
- Guide to International Legal Research, Lexis Advance
By the George Washington University Law School International Law Review. See §§ 1.04 , , .