Human performance is a key factor in the operation of many systems: for example, in nuclear power installations and in transport. The topics discussed in this volume are of both theoretical and practical importance. The contributions were presented and discussed at a Royal Society meeting in June 1989 and will also appear in the Society's Philosophical Transactions series B in 1990. Together they provide a valuable survey of areas in which research of special significance is being done. This volume will be of interest to psychologists in universities and in industry and to others concerned with practical aspects of environmental risk, work design, and complex human-machine operations.