Unlike most other identity variables, homosexuality is invisible. Western culture may have developed a complex and elaborate range of codes by which we identify homosexuality—from voice (lisps) and gestures (limp wrists) to hair styles and clothing (gay male flamboyance, lesbian dungarees)—but these remain only suggestions. The codes are transient and could, indeed, be adopted by anyone. This means that homosexuality can easily remain hidden and that its revelation can truly come as a shock. Outing is the activity of exposing someone's homosexuality; the shifting forms it has taken over the twentieth century are indicative of changing attitudes towards sexuality.

Given that lesbians and gay men have endured a history of persecution due to their sexual orientation, the ability to "hide" homosexuality is a useful survival tool. Over the course of the twentieth century, homosexuality has been culturally conceptualized as, variously, an illness, as "unnatural," and as...