Paul Bunge Prize 2011. – This work systematically investigates and reconstructs the practical knowledge Galileo shared during his lifetime. Galileo shared many aspects of practical knowledge. These included the methods and experience of foremen and engineers active within various frameworks. Galileo did not always react to such scientific impulses in the same way. On the one hand, he not only shared practical knowledge, but also acted as an engineer, especially within the framework of the art of war at the end of the sixteenth century, and more so during the time he spent in Padua. On the other hand, his scientific achievements were largely based on and influenced by aspects of practical knowledge coming from particular disciplines and activities, without him ever becoming an expert in these disciplines. Two case studies, the first concerned with Galileo's theory of the strength of materials and the second with his achievement of an atomistic heat doctrine, enable a focus on the early modern model of generation of new scientific knowledge based on the conflicting interaction between aspects of practical knowledge and Aristotelian theoretical assumptions. – This text emphasizes three main points : – 1. Galileo’s activities as a practitioner: the side of Galileo’s work historians did not relate; – 2. The practical knowledge shared by Galileo and from which his science emerged; – 3. All of the relevant letters from Galileo’s correspondence that provide an understanding of Galileo as an engineer. These are translated into English for the first time [Sources: Galileo's correspondence translated into English (38 letters)]. – Contents : Introduction. – First section: War and Practice (Chapter I: Artist-engineers' Apprenticeship and Galileo; Chapter II: Instruments and Machines; Chapter III: Galileo's Private Course on Fortification). – Second section: Practice and Science (Chapter IV: The Knowledge of the Venetian Arsenal; Chapter V: Pneumatics, the Thermoscope and the New Atomistic Conception of Heat). — Third section: The Engineer and the Scientist (Chapter VI: Was Galileo an Engineer?). – Sources: Galileo's correspondence translated into English (38 letters).