In sustainability science, the tension between more descriptive–analytical and more process-oriented approaches is receiving increasing attention. The latter entails a number of roles for researchers, which have largely been neglected in the literature. Based on the rich tradition of action research and on a specific process-oriented approach to sustainability transitions (transition management), we establish an in-depth understanding of the activities and roles of researchers. This is done by specifying ideal-type roles that researchers take when dealing with key issues in creating and maintaining space for societal learning—a core activity in process-oriented approaches. These roles are change agent, knowledge broker, reflective scientist, self-reflexive scientist and process facilitator. To better understand these ideal-type roles, we use them as a heuristic to explore a case of transition management in Rotterdam. In the analysis, we discuss the implications of this set of ideal-type roles for the self-reflexivity of researchers, role conflicts and potentials, and for the changing role of the researcher and of science in general.