The chapter offers a brief discussion of Aristotle’s theory of animal self-motion and the conception of animal agency this theory implies. I start with a description of the philosophical problem Aristotle faces in accounting for animal self-motion. His solution to that problem, I argue, lies in a biological conception of the soul as the unmoved mover of the animal’s self-motions. His theory, I further argue, includes a biological account of desire as a process that may be described as a homeostatic mechanism of self-preservation on the level of perceivers. I then turn to the resulting conception of animal agency. Here I argue that Aristotle regards animals as self-movers insofar as they appropriate, and redirect, the energy they receive from the environment for their own purposes and in accordance with how they perceive things in the world. An Aristotelian account of the causation of an episode of animal self-motion will thus have to include reference to how things appear to the animal. I end the chapter with a brief discussion of the relation of Aristotle’s biological account of animal self-motion to his account of (rational) human self-motion.