In this essay we introduce this special volume on the role of religion in world conflict. We develop a common definition of religion which focuses on five ways religion can influence society an politics: (1) as a basis for identity; (2) as a belief system that influences behavior; (3) through formal religious doctrines; (4) as a source of legitimacy; and (5) through its religious institutions. We discuss why the issue of religion has in the past received little attention from social scientists. Finally, we develop a set of common questions which the other authors in the volume address. These questions are designed to create a better understanding of the role religion plays in world conflict as well as how international relations theory can help us understand this role.