As experts and participation are influential concepts in ergonomic change efforts this paper aims at increasing the understanding of the different types of expertise needed and their relation to participation in such efforts. Drawing on experience from 15 case studies and the literature on participatory ergonomics as well as on ergonomists’ roles, a model on different expert roles is suggested. It is concluded that experts’ assumptions on how change happens must be regarded as well as the need to adapt the roles taken to the contextual conditions. Moreover, the participants’ expert role in implementation cannot be taken by outside experts.