The Moral Equivalent of War, the last public utterance of William James, is significant as expressing the opinions of a practical psychologist on a question of growing popular interest. For the past fifteen years the movement for promoting international peace has been enlisting the support of organizations and individuals the world over. That this is a question on which much may be said for the opposition, James, though a pacificist, admits with his usual fair-mindedness, pointing out that militarism is the sole nourisher of certain human virtues that the world cannot let die, and that until the peace party devises some substitute, some moral equivalent, for the disciplinary value of war, their utopian goal is neither desirable nor possible. His own solution is advanced not as a practical measure, but merely as an illustration to show that the world is full of opportunities for the peaceful development and continuation of the martial qualities of human life.