This paper examines the effectiveness of congressional involvement in shaping U.S. foreign policy toward Taiwan and discusses the role of Congress in Taiwan policy making between 1979 and 2020 through a mixed-method analysis. Although congressional involvement in Taiwan issues has shifted across different eras, it has effectively influenced the formulation and amendment of Taiwan policy by establishing legal frameworks and exerting pressure over decades. However, not all congressional behaviors are consequential. Key bills and legislators have played a more crucial role in this process. Since 2016, Congressional involvement in Taiwan issues has shown an increasing trend, and Congress has assumed a more significant share of decision-making power, adding a level of uncertainty to U.S.-China relations and cross-Strait relations. Based on the findings, this paper emphasizes the necessity of recognizing the importance of congressional involvement in Taiwan issues and calls for further research into Congress's influence on U.S. foreign policy towards specific regions and the interaction between branches.