In this chapter, I articulate and defend several views that play important roles throughout the remainder of the book. First, I articulate the task of a metaphysical theory of action as that of providing an account of the distinction between actions and mere behaviours. I then distinguish two things we might mean to talk about when we talk about someone’s actions: the things they do; and their particular doings of those things. I argue that we are ontologically committed to entities of both types, and defend my preferred ontology, according to which particular doings are events, while the things we do are a kind of property we possess.