Language is just one particularly highly developed form of primate communication. Recent years have seen increased attention to other forms: studies of animals in the wild, efforts to teach sign language to apes. This volume reflects perspectives from a variety of disciplines on the nature and function of primate signalling systems. Monkeys and apes, like people, live in a world in which they are constantly receiving and transmitting information. How can we interpret the ways in which they process it without imposing our own language-based categorizations? The problem is partly scientific, partly conceptual: that is, partly concerned with what language is. The authors' findings and insights will be of interest to a broad group of primatologists, linguists, psychologists, anthropologists and philosophers.