Classification was an important aspect of the 17th and 18th century development of Western science, epitomized by Linnaeus’s 1735 Systema Naturae (Nature’s System), in which he divided each kingdom of nature into classes, orders, and species. Linnaeus, a physician in addition to being a renowned taxonomist, endeavored to classify all known human diseases, largely on the basis of symptoms, in his 1759 Genera Morborum (Varieties of Diseases). We focus on his classification of mental disorders, a large subset of the Genera Morborum. We compare and contrast the Linnaean system with François Boissier de Sauvages’s 1772 Nosologie méthodique (A Systematic Nosology) and Rudolph Augustin Vogel’s 1764 Generum Morborum (Varieties of Diseases). We consider the impact of these nosologies on William Cullen’s (1769/1800) Nosology, a popular system of disease classification that persisted through much of the 19th century.