When a young international lawyer was confronted with legal questions during the First World War concerning war crimes, reprisals and the responsibility of States for breaches of the laws of war, he instinctively sought judicial guidance; “[t]he judgment of a Hague Tribunal”, Cyril M. Picciotto wrote, “would be of the greatest assistance”.1 This remains a common approach for practitioners and scholars of international humanitarian law, as courts, particularly international courts, have played a formative role in the development and elaboration of international humanitarian law. The body of law created to regulate wartime conduct, and famously described by Hersch Lauterpacht as being “at the vanishing point of international law”,2 has been the subject of considerable judicial attention throughout its history, and contemporary international courts are now frequently called upon to adjudicate on legal matters relating to armed conflicts. The contribution of judicial bodies to the development of international humanitarian law is the subject of this book.