Neurons that are specifically tuned to binocular depth were discovered in seminal work published 50 years ago by Horace Barlow, Colin Blakemore and Jack Pettigrew in the Journal of Physiology. Their study in the primary visual cortex opened up the era of understanding the physiology of 3-D perception. Thanks to more recent work, we now know that large areas of the extrastriate visual cortex are involved. Sites where binocular stereoscopic depth is integrated with other visual information can be identified and physiological signals related to active perceptual decisions about depth can be isolated. At some sites, a causal role of physiological signals for the perception of depth can be demonstrated by showing that weak electrical microstimulation of the cortex can alter behavioural reports of depth perception. However, there seems to be no single brain module that is responsible for computing stereoscopic depth. This lecture will trace these paths of discovery in human and animal studies. Andrew Parker will show how a better understanding of the physiology of depth perception changes our view of how the brain constructs a representation of the space around us. Findings from this neurophysiological research have implications for the growing popularity of 3-D cinema and immersive virtual reality.