Abstract
In recent years, citizens' and civil society engagement with science and technology has become almost synonymous with participation in institutionally organized formats of participatory technology assessment (pTA) such as consensus conferences or stakeholder dialogues. Contrary to this view, it is argued in the article that beyond these standardized models of "invited" participation, there exist various forms of "uninvited" and independent civil society engagement, which frequently not only have more significant impact but are profoundly democratically legitimate as well. Using the two examples of patient associations and environmental and consumer organizations in the field of nanotechnology, it is illustrated that interest-based civil society interventions do play an important role in the polycentric governance of science and technology. In conclusion, some implications for the activities of TA institutions and the design of novel TA procedures are outlined.