A paper which draws upon the experience that the Rail Accident Investigation Branch (RAIB) has gained since it became operational in October 2005. It firstly shows how human factors have featured in the causation of accidents where specific railway-related activities such as train driving or trck maintenance are taking place. It then focuses on the problem of fatigue and shows how it can affect many railway activities and be implicated in the occurrence of accidents. The overall message from this paper is that railway accident investigations provide a useful source of data on human factors issues and their impact on railway safety.