This article argues that Airbnb should be understood as a new urban institution that is transforming relations between market, state, and civil society actors. Taking the Airbnb Citizen advocacy initiative as my case, I examine how this transnational “home sharing” platform achieves such transformations, which in turn requires an investigation into the specific nature of Airbnb as an institutional form. Assuming the agenda-setting role of the urban “regulatory entrepreneur,” Airbnb aims to co-shape the terms of current and future policy debates pertaining not just to home sharing/short-term rental but also to the very fabric of city life. It pursues this mode of “platform urbanism” by mobilizing its user base, which it frames as a community of entrepreneurial middle-class citizens looking to supplement their income in a climate of economic insecurity and tech-enabled opportunity. Yet, who is the “Airbnb Citizen” and what are the opportunities and risks associated with platform-mediated citizenship?