How should scientific conclusions -- the findings on which the scientific community comes to agree -- influence our social practices and policies? How should the conduct of scientific research be influenced by the values and aspirations of the broader public? The relative paucity of research into diseases that affect the world"s poor, controversies over the teaching of evolution, the marketing of genetically modified organisms, and the reality of anthropogenic climate change make these questions urgent. They arise because there is a lack of any serious agreement about the best way to integrate scientific expertise and democratic values. The aim of this discussion is to recommend solutions for this issue and to outline ways in which scientists might approach some of the difficult practical choices with which they are confronted.