This book offers the first thorough-going account of the covert manuscript dissemination of a pivotal text in the history of early modern philosophy and science, namely the Traité de l’homme by René Descartes, completed in 1633 but published in printed form only in 1662 and 1664. This account serves as both introduction to and commentary upon the following transcription of a Latin handwritten translation of the treatise (Tractatus de homine a Cartesio) recently brought to the attention of scholars, and which was integral to such dissemination. Included is an apparatus of variants with respect to its first editions. Importantly, during its first dissemination the treatise fostered the development of medical theories based on mechanical ideas and is now increasingly at the centre of the attention of historians, thanks to the renewed appreciation of Descartes as a scientist rather than as a metaphysician. By developing an investigation taking into account not only professors and scientists, but also the importance of women, courtiers, publishers, soldiers, and the covert circulation of knowledge in the early modern age, this book contributes to the knowledge of scholars, students, and anybody interested in the early modern history of philosophy, science, intellectual history, and the history of the book in a crucial phase of the development of western thought.