A collaboration between a philosopher and an international relations scholar, this work examines the philosophical issues that underlie the theory of international relations. Part I focuses on the dominant theories of Idealism, Realism, and Behavioralism, and Part II examines the international system, the state, bureaucracies, and the individual--four factors commonly assumed to account for international behavior. The authors conclude with a summary of the links between the two forms of analysis and an open-ended assessment of their relative merits which will stimulate further discussion.