As a major developed economy in East Asia, Japan has played a complex and shifting role throughout the thirty-year history of global climate governance. This chapter systematically examines the evolution of Japan's climate policies, their underlying motivations, and their outcomes from the early 1990s to the present. The analysis reveals that Japan's participation in climate governance has been driven by a combination of its strategic pursuit of political power, energy security realities, domestic experience with natural disasters, and changes in the international landscape. Its trajectory exhibits distinct phases, transitioning from an “Active Explorer” to an “Ambitious Frontrunner,” and then to a “Cautious Participant.”