Social movements are conventionally understood as a means by which groups seek to resolve collective grievances outside of the regular political process. With this in mind, I explore the important role of ''institutional activists'' -insiders with access to resources and power -who proactively take up causes that overlap with those of grassroots challengers. This article focuses on the history of, and recent developments in, the study of institutional activism, situating the concept within existing social movement theory and providing examples of the varying roles of institutional activists in mobilization.