Unique in perspective, this text summarizes the achievements, problems, and prospects for theory in the field of international politics—with a focus on the theoretical and epistemological issues that divide the major theorists. It summarizes major theoretical approaches starting in the Middle Ages, places them in theoretical traditions, and suggests how theory evolves over time. It ends on a cautious note—praising the growing interest in the subjective dimension of the field while criticizing the wholesale rejection of empiricism by postmodernists, public choice theorists, and others.