Constitutivism is the view that we can derive substantive normative conclusions from an account of the nature of action. Agency and the Foundations of Ethics explains the constitutivist strategy and argues that the attractions of this view are considerable: constitutivism promises to resolve longstanding philosophical puzzles about the metaphysics, epistemology, and practical grip of normative claims. Yet constitutivism faces a challenge: it must employ a conception of action that is minimal enough to be independently plausible, but substantial enough to yield robust normative results. The current versions of constitutivism fall short on this score. However, we can generate a successful version by employing a more nuanced theory of action. Drawing on recent empirical work on human motivation as well as a model of agency indebted to the work of Nietzsche, the book argue! s that every episode of action aims jointly at agential activity and power. An agent manifests agential activity if she approves of her action, and further knowledge of the motives figuring in the etiology of her action would not undermine this approval. An agent aims at power if she aims at encountering and overcoming obstacles or resistances in the course of pursuing other, more determinate ends. These structural features of agency both constitute events as actions and generate standards of assessment for action. Using these results, the book shows that we can extract substantive normative claims from facts about the nature of agency.