This report reviews conceptual and practical issues associated with the design, operation, and performance of advanced systems and the impact of such systems on the human operators. The development of highly automated systems has been driven by the availability of new technology and the requirement that operators safely and economically perform more and more activities in increasingly difficult and hostile environments. It has become obvious that the workload of the operators, particularly their mental workload, may become a major area of concern in future design considerations. There has been, however, little research to determine how automation and workload relate to each other, operators of highly automated systems will impose increased mental workload. The relationship between performance and workload, which is poorly understood at best for relatively simple tasks, will be discussed in relation to highly complex and automated environments.