International audienceIn this article we explain how our team of anthropologists and information scientists worked on Michel Foucault's characteristic set of handwritten material : mainly reading cards, bibliographical and subject cards that Michel Foucault wrote, filed and used before writing his essay Les Mots et les choses. This digitized sample of his private "working library", kindly lent to us by Daniel Defert constitutes an exceptional medium to investigate, discover and analyze how Foucault used primary and secondary sources for his writing : how he read them, extracted from them, adapted them in his handwritten transcriptions (translated/endorsed/refuted/ etc.) and finally transformed this transcriptions into his final work(s). Eve...