This book is the first study of Aristotle's theory of generation and its revival by Averroes (1126-1198). For the first time, major treatises by Averroes on the physics, theory of elements, and biology of Aristotle are considered in their mutual relationship and in their connection to metaphysics. This study reveals issues at the foundation of Averroes' philosophy and reinterprets them as fundamental milestones in the history of philosophy.