In Chapter 5 we considered how the “raw” primal sketch-description of edge and line segments, terminations, and other key features-may be derived from an array of intensities in the retinal image. In this chapter we turn to consider how the primal sketch is completed by organising such low-level descriptions into larger perceptual “chunks”. When we view the world we do not see a collection of edges and blobs-unless we adopt a very analytical perceptual attitude-but see instead an organised world of surfaces and objects. How is such perceptual organisation achieved? How do we know which parts of the visual information reaching our sensory apparatus belong together? These are the questions addressed in this chapter. The first part of the chapter concentrates on human perception, since it was through the study of this that many of the principles of perceptual organisation became established. We return to the broader perspective of animal vision when we consider how such perceptual principles may be exploited in natural camouflage and advertisement. In the final part of the chapter we describe some of the principles derived from work on artificial intelligence and we review recent developments in understanding the neurobiological basis of perceptual organisation.