Studies of error and adverse events in medicine have brought a growing awareness of the extent of harm to patients. The psychology of human error strongly suggests that individual liability to error is strongly influenced by the conditions and organisation of the working environment and the nature of the task, in particular the complex and inherently uncertain judgements frequently made in medicine. Research into accidents in medicine and other high risk areas has lead to a much broader concept of causation, with less focus on individuals and more on pre-existing organisational factors. These ideas have been adapted to practical use in healthcare in the analysis of adverse events and in working towards developing safer systems of care. The final section of the paper summarises the implications of this approach for healthcare in terms of an overall systems approach, the need for basic information about clinical incidents, the benefits of systematic investigation and analysis, the nature of safety interventions, the need to study success as well as failure and the need to develop an open, safety aware culture in healthcare.