Citizens’ self-mobilization has received considerable attention in literature on land use policy and environmental politics. Involved in this mobilization process is a group of highly engaged citizens, which are known by a variety of names in literature and acknowledged for their role in policymaking. To better understand this group of policy actors, the paper investigates the motivational factors that lead this group of citizens to invest numerous hours in policymaking. The case of the planning process of a radioactive waste repository in Denmark is used, since this topic is a well-known policy struggle in many countries. Bringing together theoretical insight into motivational factors, empirical data from a nationwide questionnaire, and interviews with a selected group of highly engaged citizens, the study shows that the most engaged citizens have a distinct set of motivational factors dominated by their perception of unfairness, collective identity, and knowledge of the case.