This is the first book in English to analyse the medical category of ‘hermaphroditism’ in Spain over the period 1850-1960. It attempts to show how the relationship between the male and female body, biological ‘sex’, gender and sexuality constantly changed in the light of emerging medical, legal and social influences. Tracing the evolution of the hermaphrodite from its association with the ‘marvellous’ to the association with intersexuality and transexuality, this book emphasizes how the frameworks employed by scientists and doctors reflected not only changing international paradigms with respect to ‘hermaphrodite science’ but also social anxieties about shifting gender roles, the evolving discourse on sexuality and, in particular, the increased visibility of the ‘sexual deviancies’ such as homosexuality and changing legislation on marriage and divorce. Finally, we hope to open a space whereby the voice of ‘hermaphrodites’ and ‘intersexuals’ themselves could be heard in the past as agents in the construction of their own destiny as figures deemed ‘in-between’ by medicine and society.