Under the reign of Carlos III the Spanish government set up ambitious expeditions to the New World in order to investigate the medical virtues of the tropical vegetation. The explorers remained in America for several years collecting numerous new species, and they brought back to Europe large collections of dried plants, botanical drawings, samples and descriptions of useful plants. The case of quinine (Cinchona) is an outstanding instance of the medical, scientific and commercial issues involved in the exploration of the New World, and is one of the several discussed in detail in the dissertation. The investigation shows how colonial mercantile policies motivated the development of pharmacy during the eighteenth century and how knowledge in particular areas of natural history such as medicine and botany was shaped by economic, political and religious interests. Scientific exploration and natural history are described as forms of appropriation. Classifying and naming plants were essential practices for the displacement and accumulation of natural objects. The elaboration and central role of visual representations as well as the publication of floras are also examined in detail. The legitimation of botanical and medical knowledge involved a process of translation from folk experience into enlightened science. In this process of certification Linnaean taxonomy and eighteenth century pharmacy had central roles. My investigation provides an analysis of these practices and of the social and political interests which made them possible. Finally, my research is concerned with the influence of scientific exploration upon the nations in which the expeditions took place. The creation of scientific traditions in the Spanish America and the practice of European science by an elite of creoles had an important effect on the history of Latin America.