Preface.--On the fourth wave: past and future in the study of international systems, by C.A. McClelland.--Explanation, predication, and forecasting in international politics, by R. Tanter.--Policy classification: a key to the comparative study of foreign policy, by C.F. Hermann.--Theorists and empiricists: the two-culture problem in international politics, by J.D. Singer.--Freedom in history and international politics, by M.A. Kaplan.--A macroscopic view of international politics, by B.M. Russett.--The actors in world politics, by O.R. Young.--The external environment as a variable in foreign policy analysis, by J.N. Rosenau.--Has modern technology changed international politics? By R. Gilpin.--Notes on the analysis of national capabilities by K. Knorr.-- Zone II as a world order construct, by R.A. Falk.--Some evidence relevant to the man-milieu hypothesis, by D.A. Zinnes.--sources of international conflict, by M. Haas.--Negotiation, regional groups, interaction, and public debate in the development of consensus in the United Nations General Assembly, by C.F. Alger.-- Status discrepancy and violence in the international system: an empirical analysis, by M.A. East.--The politico-military approach to American foreign policy, by B.M. Sapin.--The Office of the Secretary of Defense and the U.S. Department of Defense, by V. Davis.--Russian interpretations of world history, by C.E. Black.