Aristotle's Nicomachean Ethics is the first and arguably most important treatise on ethics in Western philosophy. It remains to this day a compelling reflection on the best sort of human life and continues to inspire contemporary thought and debate. This Cambridge Companion includes twenty essays by leading scholars of Aristotle and ancient philosophy that cover the major issues of this foundational text. The essays in this volume shed light on Aristotle's rigorous and challenging thinking on questions such as: Can there be a practical science of ethics? What is happiness? Can we arrive at convincing accounts of virtues? Are we responsible for our character? How does moral virtue relate to good thinking? Can we act against our reasoned choice? What is friendship? Is the contemplative life the highest kind of life?