These volumes contain the papers presented at the 4th International Conference on Probabilistic Safety Assessment and Management (PSAM 4), held in New York City in September 98. The conference provided a forum for the presentation of innovative methods and applications of risk-based approaches to improve the design and operation of technological systems and processes from the economic and safety points of view. Papers reflect progress made on methods and applications in such areas as modeling and analysis of complex systems, human and organizational performance assessment, software reliability, data collection and analysis, expert judgement modeling and use, identification and assessment of various types of uncertainty, risk-informed regulatory and operational decision making, and public perception of risk. A diverse range of disciplines are represented including aerospace, nuclear, fossil fuels, chemical systems, marine technology, transportation, information technology, medical systems, environment, and defense.