What is a perversion? This talk starts by exploring psychiatric and sexological debates about perverted sexual desires from the late nineteenth century textbooks to diagnostic manuals in the twenty-first century. It looks at the role of law, morality, and medicine. Who has the power to decide what sexual acts are 'normal' or 'abnormal'? By what mechanisms do sexual practices move from one category to the other? How have people labelled 'perverse' effectively challenged their status in society?