I now want to turn to the generation of biological substances in the Generation of Animals. I have stressed the fact that Aristotle treats living things as substances ‘most of all’ (Metaph. 1034a3–4) and so biological generation should be seen as substantial generation par excellence. This forms the focus of the next two chapters. The central aim of the discussion is to set out in detail what I shall call Aristotle’s “reproductive hylomorphism”, which is a more specific application of the basic hylomorphic model from the foundational works to the generation of living things. By way of introduction I shall begin with some remarks about the project of the GA itself.