Resources for the Future and the Institute for Global Environmental Strategies convened a one and one-half day workshop on domestic and international climate policy May 11-12, 2005, in Tokyo, Japan. The first day included 49 participants hearing presentations from 13 speakers and discussing domestic activities, economics, and politics. The second day included a smaller group of participants listening to a panel of four experts and discussing opportunities for future international climate regimes. Participants included government officials from the Japanese Ministry of the Environment; the Japanese Ministry of Economy, Trade and Industry; the U.S. Environmental Protection Agency; the U.S. Department of State; and the Massachusetts Department of Commonwealth Development; representatives from business and environmental groups; and academic experts. Over the course of both days, it was clear that great opportunities exist for regularly informing experts from both countries on recent policy developments, economic analyses, and political nuances in the other country. For example, U.S. participants had an opportunity to learn the process through which Japanese technology standards are set and implemented, the subtle evolution of mandatory policy discussions, and details of current policies on voluntary trading and an emission registry. Japanese participants benefited from a frank discussion with U.S. experts of how and why it would be difficult to link different domestic emissions trading markets, the current process to establish a regional emissions trading program, and the evolving dynamics in the U.S. Senate. Looking forward, important lessons may be taken from past negotiating experiences. A small group of national leaders, including large emitters of greenhouse gases and major economies, addressing not only climate change but also developmental issues, could be a useful vehicle for meaningful international efforts. Such a small-group process should be carried out in parallel with the multilateral United Nations Framework Convention on Climate Change process. In addition, policies in both the United States and Japan reflect a strong emphasis on technology development and commercialization; this may be an area where bilateral cooperation could be particularly beneficial.