The ensuing article is based upon a lecture, the last of a series of three, delivered at the Graduate Institute of International Studies, in Geneva, in October and November of 1963. The author would like to take this opportunity to express his grateful thanks to Mr. Jacques Freymond the Director of the Institute, at whose invitation the lectures were delivered, and by whose kind permission the following article is published in this Review.The three lectures were devoted to the general theme of Christianity and war. More specifically, they endeavoured to deal with the contribution rendered by Christian ideals and thinking to the rudimentary development of the Law of War at a time when theology, morals, and law were not severable. It is from this rich amalgam that Public International Law in general, and the Law of War in particular, emerged as an integral part of the Christian civilization of Western Europe. The subsequent movement whereby International Law reached out from Europe to become more truly universal is still in progress today.