The purpose of this study is to explore the United States interests, policies and security commitments to the Republic of China (ROC) from 1949 to 1998 that have developed substantively since 1949. From the historical perspective, the principles of the U.S. dealing with the ROC military issues have altered over time relevant to its own national interests, various leaders' decision, the changing in temational system and military confrontations between the two sides of the Taiwan Strait. Historical events have been crucially examined to see how the ROC and the U.S. have maintained a substantive relationship in confronting any potential threat from the PRC. What have been the American interests, policies and security commitments to the ROC in the past and present is the main attempt of this study.