The prologue explains the meaning of involuntary sterilisation and castration and traces the origins of the practices back to the rise of the eugenics movement. It provides an overview of how involuntary sterilisation and castration have intersectionally targeted marginalised groups in different countries and sketches out how these laws and practices globally have prioritised assumed public interests over individual ones. Doing so, the prologue follows how medico-legal experts and public authorities have defined healthy and unhealthy bodies and behaviours throughout the twentieth century.