This book explores a distinctive feature of ancient philosophy: the close relation between ancient ethics and the study of the natural world. Human beings are in some sense part of the natural world, and they live their lives within a larger cosmos, but their actions are governed by norms whose relation to the natural world is up for debate. The essays in this volume, written by leading specialists in ancient philosophy, discuss how these facts about our relation to the world bear both upon ancient accounts of human goodness and also upon ancient accounts of the natural world itself. The volume includes discussion not only of Plato and Aristotle, but also of earlier and later thinkers, with an essay on the Presocratics and two essays that discuss later Epicurean, Stoic, and Neoplatonist philosophers.