This volume aims to provide the reader with an up-to-date account of knowledge, research, education, and clinical practice in the field of au tism, from an international perspective. The emphasis throughout is on the growing points of knowledge and on the new developments in prac tice. We have tried to keep a balance between the need for rigorous research and systematic evaluation and the importance of expressing new ideas and concepts so that they may influence thinking at a stage when questions are being formulated and fresh approaches to treatment are being developed. The book had its origins in the 1976 International Symposium on Autism held in St. Gallen, Switzerland but it is not in any sense a proceed ings of that meeting. Most papers have been extensively rewritten to provide a fuller coverage of the topic and also to take account of the issues raised at the meeting. Discussion dialogues have been revised and re structured to stand as self-contained chapters. Many significant contribu tions to the conference have not been induded in order to maintain the balance of a definitive review; however a few extra chapters have been added to fill crucial gaps 0 We hope the result is a vivid picture ofthe current state of the art. As editors we have been most impressed by the advances since the 1970 international conference in London.