How can decisionmakers charged with protecting the environment and the public’s health and safety steer clear of false and misleading scientific research? Is it possible to give scientists a stronger voice in regulatory processes without yielding too much control over policy, and how can this be harmonized with democratic values? These are just some of the many controversial and timely questions that Sheila Jasanoff asks in this study of the way science advisers shape federal policy. In their expanding role as advisers, scientists have emerged as a formidable fifth branch of government. But even though the growing dependence of regulatory agencies on scientific and technical information has granted scientists a greater influence on public policy, opinions differ as to how those contributions should be balanced against other policy concerns. More important, who should define what counts as good science when all scientific claims incorporate social factors and are subject to