Since the late twentieth century, “citizen science” has become an increasingly fashionable label for a growing number of participatory research activities. This paper situates the origins and rise of the term “citizen science” and offers a new framework to better understand the diversity of epistemic practices involved in these participatory projects. It contextualizes “citizen science” within the broader history of public participation in science and analyzes critically the current promises—democratization, education, discoveries—emerging within the “citizen science” discourse. Finally, it maps a number of historical, political, and social questions for future research in the critical studies of “citizen science.”