Christine M. Korsgaard presents an account of the foundation of practical reason and moral obligation. Moral philosophy aspires to understand the fact that human actions, unlike the actions of the other animals, can be morally good or bad, right or wrong. Few moral philosophers, however, have exploited the idea that actions might be morally good or bad in virtue of being good or bad of their kind - good or bad as actions. Drawing on the work of Plato, Aristotle,and Kant, Korsgaard develops a theory of action and interaction that supports this conclusion. Through action and interaction, we constitute our own identities, and Korsgaard argues that we cannot do this successfully without moral integrity.