This important book brings recent findings and theories in biology and psychology to bear on the fundamental question in ethics of what it means to behave morally. It explains how we acquire and put to work our capacities to act morally and how these capacities are reliable means to achieving true moral beliefs, proper moral motivations, and successful moral actions. By presenting a complete model of moral agency based on contemporary evolutionary theory, developmental biology and psychology, and social cognitive theory, the book offers a unique perspective. It will be read with profit by a broad swathe of philosophers, as well as psychologists and biologists.