The International Committee of the Red Cross (ICRC) is regarded as the “guardian” of the Geneva Conventions and the various other treaties that constitute international humanitarian law. The ICRC’s page on War and International Humanitarian Law is a treasure trove of information about all aspects of international humanitarian law and the law of war. In addition to providing guidance and background information about the topic, it has links to the ICRC’s research databases on treaties, customary international humanitarian law, and national implementation of international humanitarian law.
International Humanitarian Law is a chapter of this database. It provides information on the major electronic sources for researching international humanitarian law.
Oxford Bibliographies - International Law has useful bibliographies on International Humanitarian Law and Detention in International and Non-International Armed Conflict.
The U.S. Army Judge Advocate General's Legal Center & School Library has digitized a wide variety of resources on military and humanitarian law relevant to United States practice.