This INSAG publication is intended to facilitate the dissemination of information on precursor events ( which would nearly always precede a serious accident at a nuclear power plant), by means of an international system for the feedback of operating experience. A fuller understanding of precursor events would further reduce the probability of accidents, and information on such events would be particularly valuable for states in which there are only a small number of nuclear facilities. This publication describes the scope and objectives of a system for operating experience feedback, and the roles of both international and national organizations in understanding precursor events and preventing accidents.