This chapter deals with the different forms of citizen involvement in debates on the evolution of waste management policies. In a context of rapid evolution of waste treatment techniques, of pressing need to reduce waste and to develop a more sustainable management system, grassroots organizations are being called on to participate in awareness-raising actions and in consultation or participatory bodies. However, the mobilised groups wish to be recognised as legitimate actors not only on the basis of their practices and knowledge of the local context but also on the basis of their competence in a specific field of public action. The results of our study thus show the importance of highlighting both the processes whereby scientific knowledge is translated into the capacity for action, and the forms of learning and “expertification” entailing mastery of the technical discourse of professionals. However, the paper shows that democratising this technical field does not simply mean improving the participation mechanisms to take account of user’s opinions. It is also necessary to make space for the positions of groups involved in the politics of expertise.