This project focuses on the 17th-century French philosopher and scientist Pierre Gassendi (1592-1655). It will attempt to clarify some particular features of the theories on (atomic) matter and motion which the French 'reviver of Epicurus' developed. More precisely, the question whether Gassendi's atoms are innately active or not, will be readdressed. Over the years, different points of view have been advanced by scholars, resulting in a rich but rather confusing ensemble. This confusion can principally be explained by the important implications an answer to the question has on both the physical and the metaphysical level. First, if atoms would be innately active, how would Gassendi combine this with his account on the motion of concrete bodies which are supposed to behave in an inertial manner? Second, in the case of innate activity, could Gassendi, who was charged with religious functions during his entire life, have removed God from his philosophical system, given that no divine agent is required when innately active atoms can cause everything? Besides, the Latin terms used to denote the activity of the atoms, especially Pondus, Gravitas and Vis, tend to cover a considerable amount of varying significations in the historical as well as the contemporary context Gassendi was working in. What could the French philosopher have meant with these terms? In order to shed light on these issues, the project intends to investigate a wide range of primary sources. More specifically, it will not bound itself to the published works in the Opera omnia (1658), as particular attention will be paid to the unpublished manuscript De Vita et Doctrina Epicuri. Furthermore, an adequate understanding of the 17th-century evolutions in the ideas on matter and motion will help to delineate the position of Gassendi in the 'Scientific' and 'Revolutionary' debate.