Studies examining the role of philanthropic foundations in advancing social change have primarily focused on the impact of foundations’ financial resources. Few scholars have analyzed how foundations also leverage social mechanisms to advance and legitimate desired change. We conceptualize philanthropic foundations as agents of change known as institutional entrepreneurs to illuminate the social mechanisms they employ in pursuit of institutional change. We study the case of charter schools within the field of U.S. public education, where foundations elevated a new organizational form—the charter management organization—by engaging in three social mechanisms: recombining cultural elements to establish the form, enforcing evaluative frameworks to assess the form, and sponsoring new professionals to populate the form with preferred expertise. We argue that foundations are distinctive due to their ability to simultaneously pursue social mechanisms that are often considered to be the realms of different types of institutional entrepreneurs.