abstract: Indivisibles, which enjoyed a dubious status in 17th-century mathematics, have been mostly studied in the context of "pure" mathematics. Yet they sometimes played a key role in the first attempts carried on in that century to give mathematical form to the laws of physics. We shall provide some examples of such early uses of indivisibles, paying particular attention to the ways in which the conceptual differences between indivisibles and infinitesimals impinged on the efectiveness of these notions when applied to physics.