Reasons for action are considerations in the light of which we act. But just what is it that we attribute to a person when we credit her with a good reason? What sort of entity is on our minds when we deliberate about what we have reason to do? This book examines this question and evaluates a number of approaches to the philosophy of reasons, including normative realism, psychologism and Humeanism. The second half of the book contains the defense of a theory of reasons influenced by the writings of Wilfrid Sellars and Robert Brandom. This theory is further developed in relation to a number of recent topics in action theory, including the Guise of the Good thesis, internalism and the normativity of reasons.