This chapter considers the place of Sigmund Freud in the formation of the earliest historical questions raised about sexuality in late-nineteenth and early-twentieth-century psychiatric and sexological thought. It then considers a range of ways historical thinkers have used Freudian concepts, as well as the grounds on which such uses have often been explicitly rejected by others. It argues that the emergence of historiography of sexuality bears only a partial and largely indirect debt to Freud, who has less often served as a model of historical inquiry and more often served to define what one should not do. Freud is commonly attributed the status of having sown the seed that enabled historiography of sexuality to emerge globally by relativizing morality and denaturalizing sexual biology in the notion of polymorphous perversity. However, this endeavour was far from assimilable to the emerging norms of early-twentieth historical inquiry, with the result that the earliest histories of sexuality found little inspiration in Freudian thought. Post-World-War-Two uses of Freudian sexual concepts by the Frankfurt School philosophers to explain the origins of Nazism within the European Enlightenment have helped less to understand the sexual politics of Nazism or the anthropology of genocide than to malign sadomasochism.