Sado-masochism emerged as a sexual category in the late nineteenth century and was a key concept in the new Sexology of the period. Richard von Krafft-Ebing first defined it in the 1886 edition of his Psychopathia Sexualis, and the term itself was based on the names of two infamous literary figures, the Marquis de Sade and Leopold von Sacher-Masoch, the one representing a desire to inflict pain and humiliation in the interests of sexual pleasure, and the other to experience it. From the start, however, there was an ambivalence about how pathological these sexual practices were. For the sexological tradition sado-masochism was clearly a Perversion, but its roots lay in an exaggeration of the normal relations intrinsic between men and women. Krafft-Ebing saw sadism as ‘nothing else than excessive and monstrous pathological intensification of phenomena – possible too in normal conditions, in rudimental forms – which accompany the psychical sexual life, particularly in males’ (Weinberg and Levi Kamel 1983: 27). Freud, paying due homage to Krafft-Ebing’s coinage, saw it in his Three Essays as a ‘sexual aberration’, but believed it occupied a special position amongst the perversions because the contrast between activity and passivity that underlay it was amongst the universal characteristics of sexual life. Krafft-Ebing himself had recognized that a pathologized description of this sexual practice was insufficient. One of his early case studies, from whom he apparently learnt a great deal in an ongoing dialogue, was an articulate advocate of sado-masochism (Oosterhuis 2000). The clinical definition, which remained influential for a long time in psychology and psychiatry, was from the start, ironically, shaped by sado-masochists themselves.