This essay examines the problem of scientist activism as a specialized form of environmental struggle. Following research on “state-society synergy,” the author argues that this framework encourages a broader view of scientist environmental activism and its socially embedded character “in between” states and civil society. Environmental research and advocacy networks crisscross the public–private divide, linking scientists to one another, to state actors, and to environmental justice groups. These collective structures are important sites for examining the opportunities and constraints to scientist environmental activism. The synergy perspective is also useful for identifying the various forms that scientist activism can take, and for assessing the consequences of scientists' collective responses to the degradation of ecosystems and human communities.