Three fundamental questions are addressed: (1) What are the effective sources of optical information for perceiving spatial relationships and events? Complex natural environments provide a plethora of information potentially related to spatial layout. Psychophysical research investigates the efficacy and perceptual processing of these potential cues to depth and events. (2) How is this information combined by the perceptual system? Viewed in isolation, individual cues typically do not fully specify the environmental properties to which they relate. In general, the rules for projecting three-dimensional layout onto the retina are unambiguously defined, whereas the inverse operation-from the image to the three-dimensional projected scene-is not. (3) Do people perceive space and events accurately? Certainly, people act in the environment as if they represent its spatial relationships accurately; however, effective action can often be achieved without geometrically correct representations. From a pragmatic perspective, perceptual representations are accurate to the degree that they provide effective guidance for behavior. This issue is developed and discussed throughout the chapter.