This book examines an important area of Aristotle's philosophy: the generation of substances. While other changes presuppose the existence of a substance (Socrates grows taller), substantial generation results in something genuinely new that did not exist before (Socrates himself). The central argument of this book is that Aristotle defends a 'hylomorphic' model of substantial generation. In its most complete formulation, this model says that substantial generation involves three principles: (1) matter, which is the subject from which the change proceeds; (2) form, which is the end towards which the process advances; and (3) an efficient cause, which directs the process towards that form. By examining the development of this model across Aristotle's works, Devin Henry seeks to deepen our grasp on how the doctrine of hylomorphism - understood as a blueprint for thinking about the world - informs our understanding of the process by which new substances come into being.