Visual information processing in humans with intellectual disabilities and in animals is presented, for conceptual and methodological reasons. Much of the evolutionary path of higher primate species has involved the development of sophisticated visual systems that interact with complex, higher-order cognitive processes. Key questions in cognitive science address the manner in which the environment is represented by the organism, and thus relate to how knowledge about the world is gleaned, with implications for theories of action and decision making. Finally, it has become apparent that the distinction between perceptual and cognitive processes is not always a clear one, and that these processes interact in critical ways in underlying complex behavioral repertoires.Consistent with the emphasis in this series on individual differences, both typical and atypical development are explored here. Philosophical approaches to visualism are also presented. Chapters have import both for basic science and for the development of applications.