Just war, international law, and world order are all historically conditioned realities that interrelate with one another in complex ways. This paper explores their historical development and current status while critically examining their interrelationship. It begins with exploring just war as a basic frame for analysis and interconnection with the other two realities. Just war is not an abstract body of moral thought but instead a practically informed morality of war rooted in Christian thought and law, Roman law, and the practice of statecraft. The essay notes the importance of the ideas of jus gentium and jus naturale in just war's fundamental formation, as well as the parallel between its three basic features—sovereign authority, just cause, and the end of peace—and the three goods or ends of politics as classically defined, namely, order, justice, and peace. The essay then moves out to explore the historical and thematic relations between just war tradition and international law, especially the law of war, arguing that these together define a moral and legal structure that is normative for world order. The final section of the paper considers the functioning of the institutions of world order in the context of challenges from rival cultural understandings of war, law, and world order and from the rise of nonstate actors in the international sphere, arguing for dialogical efforts aimed at strengthening both the moral and legal basis for world order against contemporary threats to that order.