Kinsey Institute (KI) librarians created Sexual Nomenclature in the 1970s as a means of improving cataloging accuracy for KI collections. This article traces the two origins of the thesaurus: Alfred Kinsey's original library organization in the 1940s and 1950s and gay and lesbian library activism in the 1960s and 1970s. Sexual Nomenclature's authors aimed to create and to deploy sex-specific terms that other libraries could use to improve user access to and knowledge of sex-related materials. An examination of Sexual Nomenclature's functionality in the past and present demonstrates both the difficulty and necessity of keeping controlled vocabularies for sexological concepts up-to-date.