The end of the Cold War posed a formidable challenge for theorists of international relations. Almost all of the theoretical approaches that were in vogue in the 1980s were unable to account for the sudden end of the bipolar Cold War system. These approaches could explain incremental change in international politics, but they fell woefully short when confronted by revolutionary developments of the sort that occurred in 1989–1991. Leading scholars in the field of international relations in recent years have sought to adapt earlier theories and devise new ones to help explain drastic changes in the international system. The books under review show that improvements and useful innovations have occurred but that the field still has a long way to go before it can fully cope with abrupt, radical change.