The postwar years have been a period of great interest in the theory of international politics. A contributor to this Review has surveyed the state of the study of that theory and indicated the alternatives open to it. Within the last year the Institute of War and Peace Studies of Columbia University has held a series of seminars on the subject in an effort to push forward research frontiers. Interest in theory is no reflection upon the merits of scholarly endeavors that are not oriented primarily to theoretical considerations. But it does assume the independent importance of a theory of international politics. The present essay assumes the importance of theory in general, but is based upon a particular kind of theory, namely, systems theory.