[en] Since the accident at the Three Mile Island nuclear power plant on March 28, 1979, the commercial nuclear industry in the United States has paid increasing attention to the role of humans in overall plant safety. As the regulatory body with primary responsibility for ensuring public health and safety involving nuclear operations, the United States Nuclear Regulatory Commission (NRC) has also become increasingly involved with the ''human'' side of nuclear operations. The purpose of this symposium is to describe a major program of research and technical assistance that the Pacific Northwest Laboratory is performing for the NRC that deals with the issues of safety at nuclear power plants (NPPs). This program addresses safety from several different levels of analysis, which are all important within the context of an integrative approach to system safety