The problem of the individual arises in Aristotle at the joining-point of the two major investigations in Greek thought, that of substantial change and that of the intelligibility of the world. It is solved within the hylemorphic framework of the composition of substances. In other respects the metaphysical concepts of the Stagirite partially underlie the study of the cosmos and that of living beings. This article shows that the Athenian thinker was not always able to move in a legitimate manner from one of theses registers of thought to another. As a result difficulties have arisen in his doctrine of the individuation of substances on the three levels of metaphysics, biology and cosmology. (Transl. by J. Dudley).Le problème de l'individu s...