||This dissertation examines Aristotle's use of the verb oregesthai, with a particular interest in instances suggestive of an ontological striving in natural teleology. Aristotle associates desire in perishable beings with the appetitive soul, yet he uses this verb in conjunction with the activity of the nutritive soul in De Anima II.4 and with the activity of the divine spheres in Metaphysics XII.7. To address this discrepancy, we advocate a consistent role for orectic striving with respect to all perishable living beings in Aristotle's theoretical philosophy. Chapter One considers the question of natural teleology in Aristotle as interpreted by recent scholars, some who reject a role for desire in this process and others who affirm it. The second chapter provides a general survey of oregesthai, and includes investigations into instances of the verb in a select group of Aristotle's predecessors: Hesiod, Homer, and Plato. We then examine the traditional understanding of the noun orexis in Aristotle as well as briefly survey oregesthai in his work. Chapters Three and Four consider De Anima II.1-4 with a view towards understanding how the unusual instance of oregesthai in II.4 unfolds from the guiding question of the treatise: what is soul? These chapters culminate in a focused analysis of the capacities and ends of the nutritive soul. Chapter Five turns to Physics I and Aristotle's assertion that matter desires form, where desire translates oregesthai. Insofar as this text concerns all perishable ousiai, we argue its conclusions to be most relevant to the nutritive soul. The heart of the chapter considers I.9 and the context in which Aristotle turns to oregesthai to help explain generation. We conclude that living matter is distinguished from inorganic matter through ontological striving as a fundamental and necessary source of all natural life.