This chapter explores, through an engagement of social science, how civil society actors can effectively pressure governments and market actors to take climate action. The chapter begins by noting the significant challenges of global climate cooperation. It then turns to social movement theory, namely political economy, resource mobilization, political opportunity structures, and framing strategies, to explore the role of civil society in influencing U.S. climate policy. It finds that progress thus far has been limited by political deadlock in Washington, as well as powerful political economic interests arrayed against climate action. Drawing on the same set of theories, the chapter takes stock of the more recent efforts by civil society to explicitly target sources of carbon emissions. It concludes that grassroots activism holds significant promise for the future of climate advocacy, though its policy impact remains to be seen. The chapter concludes with avenues for future research.