Probabilistic safety assessment (PSA) has contributed significantly to the understanding of how best to ensure the safety of nuclear power plants. By means of PSA a nuclear power plant, including its safety systems and installations, can be analysed in its entirety. The rapid development of the method has resulted in its extensive use. This report reviews the general bases of PSA, emphasizing its merits and limits as well as the general lines of the future development of that methodology and its applications. Contents: 1. Introduction; 2. Capabilities and limitations of the methodology of PSA; 3. Further development of methodology; 4. Guidelines for presentation and interpretation of PSA results; 5. How should PSA be used in the future?; 6. Conclusions.