This article reviews the potential contribution of deliberative theory and actor network theory to the practice of social impact assessment (SIA). With reference to a case study of the World Commission on Dams, it argues for an approach to SIA that goes beyond documenting social change and that (1) targets consensus building among those impacted by planned interventions as a basic starting point for social scientific investigation; (2) places greater emphasis on the ways in which peoples’ values, aspirations, perceived interests, and political coalitions change throughout the life of a proposal and shape their experience of project outcomes; (3) seeks to unravel the often unstated assumptions about who and what is important that are built into social data and stakeholder representative structures; and (4) challenges the separation of the ‘‘social’’ and the ‘‘natural’’ by fostering a more productive engagement between scientific and lay knowledges about the processes and impacts of change.