Environmental activists are an important voice in public and private politics, urging governmental and corporate responses and solutions to ongoing environmental damage. Scholars have become increasingly interested in understanding environmental movements and the influence of environmental activist organizations. This article describes two literatures that have analyzed the dynamics and outcomes of activism, one based in a sociological examination of social movements and the other in economic analysis of activist nongovernmental organizations. Although the literatures sometimes use different language and methods, they have much in common. We highlight the consistent themes—in particular the shared respect for the rational actor model—the particular strengths of each tradition, and directions for future research where synergies between the disciplines could be more fully exploited.