Since the end of the Second World War, industrial and medical uses of radiation have been considerably increasing. Accidental overexposures of persons, in either the occupational or public field, have caused deaths and severe injuries and complications. The rate of severe accidents seems to increase with time, especially those involving the public; in addition, accidents are often not immediately recognised, which means that the real number of events remains unknown. Human factors, as well as the lack of elementary rules in the domains of radiological safety and protection, such as inadequate training, play a major role in the occurrence of the accidents which have been reported in the industrial, medical and military arenas.