This study, which explains theorizing in perception, pays particular attention to vision. Describing three pieces of research work which have won the Nobel Prize, the text observes perception at work in daily life and explains how readers can be trained to increase their awareness. Subjects covered include the three-factor and opponent-process theories of colour and vision, neural processes in the retina, the Gestalt theory, ecological optics and the computational theory of vision. Although the text has been aimed primarily at undergraduate psychology students, it has been written in a straightforward manner which should also be of benefit to students in related disciplines, such as philosophy and physiology.