This article sets out to throw light on the intellectual and scientific activities of a group of Spanish humanists associated with the diplomat, aristocrat, and writer Diego Hurtado de Mendoza in the course of his fifteen years in Venice, Trent, and Rome, focusing on two aspects that have been neglected to date. These are (a) the integration of practices connected with the study of nature (herborizing expeditions and the production of herbaria) with the work of collating, translating, and commenting on classical texts dealing with natural history and materia medica; and (b) the insertion of these scientific activities in Italy by the Spanish subjects of the Emperor Charles V within the broader context of a specific cultural policy. This policy would later be fleshed out in the scientific project of the Spanish Crown under Philip II, inseparable as it was from the monarch’s political and religious policy.