Ripstein’s lectures, which constitute the central texts of this book, focus on the two bodies of rules governing war: the ius ad bellum, which regulates resort to armed force, and the ius in bello, which sets forth rules governing the conduct of armed force and applies equally to all parties. The lectures argue that both sets of rules constitute prohibitions rather than permissions, and that recognizing them as distinctive prohibitions can reconcile the seeming tension between them. By understanding that the central wrong of war is that war is the condition which force decides, Ripstein contends that the law and morality of war are in fact aligned; the rules governing the conduct of hostilities must apply equally to parties in the right and parties in the wrong in an armed conflict, because the prohibitions outlined in the rules governing war are prohibitions that restrain war. Ripstein’s method of analysis and the substantive argument he puts forward offer an opportunity for rigorous critical engagement in subsequent essays by commentators Hathaway, Kutz, and McMahan, followed by a response from Ripstein.