What an agent does, as opposed to what happens to an agent (or even what happens inside an agent’s head). Describing events that happen does not of itself permit us to talk of rationality and intention, which are the categories we may apply if we conceive of them as actions. We think of ourselves not only passively, as creatures within which things happen, but actively, as creatures that make things happen. Understanding this distinction gives rise to major problems concerning the nature of agency, of the causation of bodily events by mental events, and of understanding the will and free will. Other problems in the theory of action include drawing the distinction between an action and its consequences, and describing the structures involved when we do one thing ‘by’ doing another thing. Even the placing and dating of action can give rise to puzzles, as in cases where someone shoots someone on one day and in one place, and the victim then dies on another day and in another place. Where and when did the murder take place?