This is an extensive collection of essays on all aspects of vision, approached from the perspective of coding and efficiency. It examines the broad spectrum of vision research from one particular, unifying viewpoint, namely the way that visual systems efficiently encode and represent the outside world. This approach, both rigorous and general, was championed by H.B. Barlow in the fifties and has been followed in many areas of vision research. The approach has recently acquired new significance due to the growing interest of computer science and artificial intelligence in the processes of vision, which attempts to describe visual processes in algorithmic terms, equally relevant to a robotic visual system, the eye of a fly or the complex visual pathways in the human brain.