Early modern European thought held that men and women were essentially the same, with social forces creating their differences. Such a view made the existence of hermaphrodites easy to accept. During the seventeenth century, medical and legal arguments began to turn against this ‘one sex’ model, with hermaphroditism seen as a medieval superstition. This book traces this change in Iberia in comparison to the earlier shift in thought in northern Europe, and with concurrent ideas in Latin America.