Customary international humanitarian law consists of rules derived over time from “a general practice accepted as law”. Customary IHL complements and fills in the gaps in treaty law. The best freely available online source is the International Committee of the Red Cross’s website on customary practice in international humanitarian law.
International Committee of the Red Cross: Customary International Humanitarian Law
The website of the International Committee of the Red Cross, which includes the Customary IHL Database for access to the rules and practice of customary IHL, as well as other materials relating to customary IHL. This website also includes a full text database version of Customary International Humanitarian Law, by Jean-Marie Henckaerts and Louise Doswald-Beck and PDF versions of Volume I: Rules and Volume II: Practices.
The database version of Customary International Humanitarian Law contains rules and practices, but is updated on a regular basis.
International Law Commission
The International Law Commission (ILC) was created in 1947 to promote the codification of international law. Researchers can find yearbooks, reports and the texts of the Commission’s other work under the website’s Research tab.