This project aims to trace the changes in the U.S. policies toward regional organization of East Asia during the cold war, using archival source materials such as declassified documents of U.S. government departments and agencies. The focus will be on the bureaucratic, domestic and international political processes on the side of the United States surrounding the establishment of regional organizations such as SEA TO, ASPAC, ASEAN, ADB and APEC, with analyses of contending views and approaches within the U.S. government. By this historical study on the postwar period, this project attempts to present a framework to understand the oscillation of United States policy between ardent encouragement and suspicious passivity toward East Asian regionalism.