This chapter examines Japan’s role in the Cambodian peace process after 1989. In that year, the long-awaited international conference to settle the conflict was held in Paris. Two years later, the conference was convened again, resulting in the signing of peace agreements. The intensified involvement of the UN Security Council permanent members in this phase of the settlement contributed to bringing the Cambodian peace process to the attention of the world community. This chapter shows how, building on a decade of diplomatic efforts on the Indochinese problem, Japan acted as one of the active players in the peace process, contributing diplomatically and financially to restore peace as well as by dispatching its Self Defense Forces to participate, for the first time ever, in the UN peacekeeping operation in Cambodia. The settlement of the Cambodian conflict removed the main obstacle to the realization of a peaceful and integrated Southeast Asia and, during the 1990s, the three Indochinese countries joined ASEAN. Japan’s role in the Cambodian peace process galvanized its confidence in promoting regional dialogue and cooperation on political and security affairs, thereby expanding the scope of Japan’s traditionally economy-focused foreign policy and contributing to shaping the emerging post-Cold War regional architecture.