While Descartes is literally present in 27 of 722 pages that Being and Nothingness counts, Hegel appears in 43, Husserl in 46 and Heidegger in 47 of them. Without asserting, and thus without infirming the obvious influence of these three German thinkers on it, one year after his essay of phenomenological ontology, it is nevertheless the filiation and the manner of only the French phi-losopher that Sartre claims in front of Pierre Lorquet. So, which relative and which model is Descartes for him? And what relationship does Sartre exactly maintain with him? Following the track of the latter in the 1943 treatise, I want to ensure that “the individual of existentialism is Descartes’s true heir.”