Abstract: In this paper I argue that Poincare’s acceptance of the atom does not indicate a shift from instrumentalism to scientific realism. I examine the implications of Poincare’s acceptance of the existence of the atom for our current understanding of his philosophy of science. Specifically, how can we understand Poincare’s acceptance of the atom in structural realist terms? I examine his 1912 paper carefully and suggest that it does not entail scientific realism in the sense of acceptance of the fundamental existence of atoms but rather, argues against fundamental entities. I argue that Poincare’s paper motivates a non-fundamentalist view about the world, and that this is compatible with his structuralism.