As agents of strategic institutional change, institutional entrepreneurs (IEs) draw resources from their structural environment to alter the structural context in which they are embedded. In this article, we explore which resources IEs mobilize in different structural settings. We distinguish between (positional or free) field resources and personal resources, all of which may be material, cultural, social, symbolic or political in kind. Our review of leading case studies of institutional entrepreneurship shows that centrally positioned IEs draw primarily on organizational positional resources. By contrast, peripherally positioned IEs rely mainly on the skilful mobilization of free resources as well as on the personal resources of individuals. Also the field’s degree of institutionalization has an impact on IEs’ resources: in emerging fields where field positions and field boundaries are not yet defined, resources must be imported from mature fields. Furthermore, although resource-poor peripheral IEs may set off institution-building processes in emerging fields, they are usually superseded by central organizational actors during later stages of institution-building.