In the sixteenth and seventeenth centuries, America’s Indigenous people provided, under different circumstances, information (or not) to Europeans and Americans about resources and commodities of the New World. Euro-Americans were particularly interested in medicinal plants. In the case of Mexico, they obtained medicinal plants and information in the markets of Mexico. In the case of Virginia and Peru, Euro-Americans had to find informants among reluctant Indigenous people. This project discusses the ways in which information about medicinal plants circulated in the Atlantic World, and how this information shaped the emerging empirical practices of early modern science.