These companion volumes will be greeted with enthusiasm by anyone interested in early modern medicine, ethnobotany, or colonial science. They make available in English translation the writings of the Spanish physician Francisco Hernandez (1515–87) and provide a series of authoritative articles analysing his work and situating it in historical context. In what was arguably the first scientific expedition in the age of European imperialism, Hernandez travelled in New Spain between 1571 and 1577 under orders from Philip II to gather information on the medicinal uses of New World plants. Over these six years Hernandez visited the major hospitals, interviewed numerous European and Amerindian informers, cared for victims of epidemic diseases, and compiled descriptions of thousands of plants and hundreds of animals and minerals. The original manuscript of Hernandez’s Natural history of New Spain—six folio volumes of text and ten containing illustrations of plants and animals—was the most complete repository of first-hand knowledge on New World materia medica at the time. It provided information on Amerindian medical knowledge, which was rapidly disappearing due to death and conversion, and also described plants that held enticing medical and commercial promise for Europeans. The Spanish crown, eager to protect such sensitive information, did not publish the manuscript, and it was destroyed by a fire in the Escorial palace in 1671. Fortunately, several copies and abstracts of Hernandez’s work existed, and his descriptions were incorporated into the publications of many well-known authors—most often unaccredited, a common practice at the time but one that has caused great trouble for scholars wishing to study his writings or assess their impact. The Mexican treasury provides English translations of a rich selection of Hernandez’s varied works, and explains the complicated trajectory of his Natural history of New Spain. The chart illustrating the fascinating and intricate history of this text highlights the enormous challenge faced by the book’s editor and translators, and the great service they have performed in providing what will from now on be the standard English edition of Hernandez’s work. Roughly half of the translations are dedicated to Hernandez’s letters to the king, his will, and extracts from his varied writings, among them Antiquities of New Spain (a description of Amerindian customs) and The Christian doctrine (a long missionary poem). The remaining translations are extracts from different incarnations of Hernandez’s natural history observations: the first published version, Quatro libros de la naturaleza (Mexico, 1615); the famous edition produced by the Accademia dei Lincei, Rerum medicarum Novae Hispaniae thesaurus (Rome, 1651); the publications of seventeenth- and eighteenth-century authors in England and the Low Countries, among them Juan Eusebio Nieremberg, Georg Marcgraf, John Ray, Hans Sloane, and James Petiver; and the Spanish edition of 1790. The decision to translate such a diverse range of texts was a fortunate one, both in terms of the wealth of material it provides for readers and the way in which it conveys the scholarly culture to which Hernandez belonged, where materia medica, religion, and philosophy were closely connected subjects. The translations are precise and clear, and while certain passages might sound somewhat stilted in their strict adherence to the original diction, the choice of precision over style is one that readers will appreciate. Searching for the secrets of nature brings together a collection of short essays describing the cultural and political setting in which Hernandez lived, the conditions of medicine in New Spain at the time he arrived there, and the reception and dissemination of his work. The first section of the book introduces the interaction between science and empire during the reign of Philip II and discusses the importance of humanism and the classical tradition within the intellectual landscape inhabited by Hernandez and his contemporaries. A second section is devoted to medical knowledge and practices in sixteenth-century New Spain, including the regulation of practitioners, the functioning of hospitals, and the onslaught of deadly epidemics that ravaged indigenous populations, truly biological weapons at the service of colonization. A third section traces the dissemination of Hernandez’s findings, analysing the reception of American drugs in Europe and the incorporation of Hernandez’s description into publications from the sixteenth to the nineteenth centuries. A postscript addresses continuing traditions of Mexican medicine and the popular legacy of Hernandez in the present day. There is much here to interest readers from a wide range of backgrounds, and the texts are remarkably rich in detail and information in spite of their brevity. These essays hold great potential for the classroom, and will prove a valuable resource for teachers interested in enriching and diversifying the curriculum with discussions of transcultural contact and non-European knowledge. A project covering so much ground will inevitably give short shrift to certain topics, and some readers will find their particular interests dispatched summarily or missing altogether—there is, for instance, very little discussion of Hernandez’s working methods, and the fascinating images he collected are regrettably ignored (although sixty-four woodcuts from the 1651 Rome edition are reproduced). But to grumble about what these volumes lack would imply a failure to recognize just how much material is provided, how well and richly it is analysed, and how many connections are drawn. In making these important materials readily available to Anglophone readers, and in explaining and contextualizing them so well, these two books constitute an immensely valuable resource.