The Swedish naturalist Carl Linnaeus (1707-1778) is best known as a botanist, for his revolutionary system of classifying plants and his new nomenclature. But Linnaeus trained first and foremost as a physician, and practiced for several years as a doctor in Stockholm in the early 1740s. Even when he was established as professor of botany in Uppsala, Linnaeus continued to investigate plants for their medicinal properties. His materia medica came to form an intricate part of his search for a natural system of plants based on their affinities. Indeed, Linnaeus was one of the first to suggest that ‘natural’ plant genera and families share similar pharmaceutical virtues, and that herbal drugs might be sought out on that basis. The numerous notebooks, manuscripts and printed works he annotated on materia medica are now kept at the Linnean Society in London. They include the manuscripts and notebooks in preparation for the works published as Materia Medica (1749), Genera Morborum (1763), Clavis Medicinae (1766), as well as a score of monographs (such as Vires Plantarum, 1747) and various other prescriptions and loose notes. They provide an excellent opportunity to investigate the links Linnaeus made between natural history and medical knowledge, two disciplines that he would probably not have recognised as distinct, and how his day-to-day work practices influenced his medical ideas. It will also throw some light on the role of materia medica in the broader history of taxonomy in the second half of the eighteenth century.