Since the late nineteenth century the human and the social sciences have had a profound impact on how Western societies have defined and sought to solve social problems. Explaining crime by reference to abnormalities of the brain, using market research techniques to modify political strategies, or employing therapeutic institutions to promote democratic citizenship - these are just three examples of how the human and social sciences have been applied since 1880. Experts from many disciplines have occupied key positions in state and society, guided political decisions, and helped to establish new social institutions and practices. Their expertise has had to compete with other forms of knowledge and has been used by politicians and social actors for their own ends. Providing a trans-disciplinary and comparative perspective, the essays in this volume address the tension between the claims to objectivity and the politicization of expert knowledge, examine the relationship between knowledge and power, and discuss long-term historical developments, transcending the political caesuras of twentieth-century.