Is Aristotle's ontology of sensible substances a constituent ontology? If so, is it—as some critics of constituent ontology assert—unintelligible? What can be said in defense of the coherence and truth of constituent ontology? In this dissertation, I offer a defense of Aristotle's constituent ontology. This defense is a defense twice over; first, against those who assert otherwise, it is a defense of the claim that Aristotle's ontology is constituent. Second, against those who assert constituent ontology's unintelligibility, it is a defense of the claim that Aristotle's ontology is not only not incoherent, but superior to many versions of Platonism.My first chapter is an introduction that contextualizes the arguments of my dissertation by reviewing the definitions of constituent and relational ontology and highlighting the features of constituent ontology that will be the focus of the main chapters.My second chapter defends a constituent reading of Aristotle's hylomorphic theory against certain contemporary Aristotelian scholars who deny that Aristotelian substances and accidental unities are composed of real and differentiated ontological parts.My third chapter investigates Peter van Inwagen's case against the intelligibility of constituent ontology—viz. that it makes a category mistake by posting genuinely located properties. I show that, according to the most important commentators on constituent ontology—Michael Loux, Nicholas Wolterstorff, and Gustav Bergmann—the genuine location of properties is neither an essential nor a coincidentally ubiquitous feature of constituent ontology; van Inwagen's argument, therefore, fails as a general refutation of constituent ontology.My fourth chapter explores the possibility that, according to Aristotle, substantial and/or accidental forms are genuinely located, and that, therefore, Aristotle's constituent ontology is susceptible to van Inwagen's attack. I argue that it is immune. The demonstration of its immunity involves investigating Aristotle's notions of place, where, and accidental location. My fifth chapter argues for the coherence and truth of constituent ontology; the former is accomplished by showing how certain common aesthetic intuitions lead naturally to the constituent ontological view. The latter is accomplished by defending the soundness of a brief argument whose conclusion is the truth of constituent ontology.