According to Gibson’s theory of visual perception, changes over time in the optic array, such as the optic flow created by our movement, provide us with the information that we need about the structure of the world around us. Gibson also argued that perception and action constrain one another; perception is the pick-up of information currently needed to guide action, and action in turn causes transformation of the optic array that yields further information for perception. In this chapter, we will bring these two aspects of the theory together to explore the role of optic flow in control of animal and human locomotion. We will consider whether global patterns of optic flow are used to solve such problems as maintaining a stable position in space, or controlling the speed and direction of movement. The evidence that we will discuss comes not only from within the Gibsonian tradition, but also from research in a range of other areas of psychology, and in biology, that has converged on the same problems.