John Money, New Zealand psychologist and sexologist, known for his research on gender identity, and responsible for controversial involuntary sex reassignment of David Reimer (died 2006)

John William Money was a New Zealand American psychologist, sexologist and professor at Johns Hopkins University known for his research on human sexual behavior and gender.

Gender identity is the personal sense of one's own gender. Gender identity can correlate with a person's assigned sex or can differ from it. In most individuals, the various biological determinants of sex are congruent and consistent with the individual's gender identity. Gender expression typically reflects a person's gender identity, but this is not always the case. While a person may express behaviors, attitudes, and appearances consistent with a particular gender role, such expression may not necessarily reflect their gender identity. The term gender identity was coined by psychiatry professor Robert J. Stoller in 1964 and popularized by psychologist John Money.

Gender-affirming surgery (GAS) is a surgical procedure, or series of procedures, that alters a person's physical appearance and sexual characteristics to resemble those associated with their gender identity. The phrase is most often associated with transgender health care, though many such treatments are also pursued by cisgender individuals. It is also known as sex reassignment surgery (SRS), gender confirmation surgery (GCS), and several other names.

David Reimer was a Canadian man raised as a girl following medical advice and intervention after his penis was severely injured during a botched circumcision in infancy.