Despite the central role these phenomena play in our lives, surprisingly little is understood about their moral significance and the concepts and values that underpin them. What does it mean, exactly, for an agent to act ‘on behalf’ of another person or group? It seems intuitive that successfully acting on behalf of others contributes to the moral justification of one’s actions. But what explains this connection? Under what circumstances do persons and groups have a right to demand that others not act on their behalf? Crucially, why (and to what extent) do such demands impose constraints on the moral justifiability of others’ actions? How do these constraints affect the moral justification of state action and public policy?