We act for reasons. But, it is sometimes claimed, the mental states and events that make up reasons, are not sufficient conditions of actions. Reasons never make actions happen. We- as agents (persons, selves, subjects) - make our actions happen. Actions are done by us, not elicited by reasons. The present essay is an attempt to understand this concept of agent causality. Who - or what - is an agent ? And how - in virtue of what - does an agent do things, or refrain from doing them? The first chapter deals with problems in the theory of action that seem to require the assumption that actions...