The standard issues with experts are about the nature of scientifi c expertise; problems of legitimacy and problems having to do with the limits of expertise; problems having to do with the place of experts in democratic politics and bureaucracies; as well as more general problems about the knowledge that experts possess: what the role of tacit knowledge and knowledge embodied in things and routines is, and to what extent expertise can be replaced or augmented by expert systems and technical means. The chapters collected in this volume will be concerned with all of these issues, with the exception of tacit knowledge and technological “expert systems,” which will be the subject of a separate volume, Understanding the Tacit. The chapters in the present volume, however, go beyond the problem of scientifi c expertise, which will be treated as one type among many forms of expertise.