The importance in social relationships of the exchange of information by non-verbal gestures and expressions, though long appreciated by artists and writers, has only recently become the subject of serious scientific study. The subject has been approached from different angles by psychologists studying the relevance of non-verbal communication to interpersonal relationships, by anthropologists interested in how these processes help to integrate societies, and by ethologists extrapolating the results of animal studies to human behaviour. The scope of the volume ranges from formal analysis of the communication process by an information theorist (Professor Mackay) and by a linguist (Professor Lyons), to accounts of the role of expression in the theatre (Dr Jonathan Miller) and in the visual arts (Professor Gombrich). There are contributions to the discussion written from the point of view of the zoologist, the ethologist, the psychologist and anthropologist.