This report addresses the topic of driver fatigue, an issue which is receiving increasing attention in the road safety field. A range of subject areas is reviewed in detail, including concepts and theories directly related to fatigue, the measurement of fatigue, factors contributing to the onset and development of fatigue, the degree to which fatigue is associated with road crashes, countermeasures having potential for offsetting the degrading effects of fatigue on safety, and an identification of research issues having promise for reducing the role of fatigue in crashes.