Recently a group of scholars, analysts, and diplomatists met for a weekend conference on theoretical approaches to international politics. Their discussion was inspired by the widespread and growing interest in conceptual and theoretical problems illustrated by parallel efforts in the study of politics, economics, law, and human relations. In the field of foreign relations the impulse toward theory comes from practitioners as well as philosophers. Indeed a former Secretary of State maintains that our most urgent need is for “an applicable body of theory in foreign policy.” Practical men with first-hand diplomatic experience point to the need for rational generalizations and intellectual structures to extract meaning from the jet stream of contemporary events. The intellectual processes by which practical judgments are made along a moving front of events clearly demand inquiry and analysis. Theory in the study of international politics perhaps derserves a special priority because of the urgency of the problem and the stridency of the debate generated by competing approaches each claiming to have preempted the field. Perhaps what is called for is a sorting out and assessment of the intellectual factors that go into diverse theories of international politics at varying levels of abstraction and generality. This sorting out was one of the objectives of the conferees. Similarly this paper seeks to review the nature and purpose of theory, its limitations, and the characteristics of the chief types of theory in international politics.