The U.S. is an important actor in international climate and clean energy politics. Over the last thirty years, however, it has oscillated between engagement and dis-engagement. This chapter explores the role of the U.S. in climate and clean energy politics, with a focus on three key questions. First, we examine the domestic factors that explain U.S. engagement and dis-engagement with international climate politics. Second, we explore the causes as well as advantages and disadvantages of different modes of foreign engagement. This includes plurilateral versus multilateral cooperation and economic competition and global trade. Third, we examine the nature and drivers of the engagement of sub-national actors, including cities, states, and corporations. Next to laying out these key theoretical debates, the chapter provides historical overviews of U.S. foreign policy on climate and clean energy. The conclusion proposes areas for future research.