This project aims to examine a crucial question related to a major philosophical and scientific shift in the Early Modern period: what is the nature of motion imparted to atoms in Pierre Gassendi’ atomistic matter theory? Pierre Gassendi (1592-1655) was one of the first and major proponents of an atomistic theory of matter in the 17th century. He advocated a revival of Epicurean atomism within a Christian context. For that reason, he came to ascribe the source of atoms’motion to God who instilled motion into matter at the Creation. But at the same time, Gassendi considered that this amounted to rejecting matter’ inertness and to attributing to matter a moving force, i.e. mobility. This project will seek to evaluate the philosophical, scientific and theological consequences of such a position for the nature of matter, the principle of inertia and the conception of natural and divine causation. By retracing the genesis of Gassendi’ conception of atomistic motion, it will show how he reached this theory: it first took root in a historical and philological project seeking to reconstruct Epicurus’philosophy, it was then enriched by Gassendi’ scientific concerns related to Galilean mechanics, and it found a final formulation in the posthumous publication of Gassendi’ Syntagma Philosophicum. To that end, a key element of this project will be to translate and to publish the as yet unpublished manuscript of Book XIII of Gassendi’ De Vita et Doctrina Epicuri "De atomis".