This report gives an account of the history of nuclear power plant safety, covering the important elements from safety in the earliest days to lessons learned from accidents and current reactor safety principles. The report concentrates on light and heavy water moderated reactors, by far the most prevalent types. It concludes that for these types of reactors, levels of safety are in reasonable agreement with the present INSAG quantitative targets for probabilities of core melt and radioactive releases. The report is directed at an educated general public. Contents: Summary; Prologue; 1. Important elements of the history of nuclear plant safety; 2. Current reactor safety principles; 3. Safety of nuclear plants; 4. Nuclear fuel cycle; 5. Features desired in future plants; 6. Continued improvement of nuclear power plant safety; 7. Conclusions; Appendix I: IAEA safeguards against proliferation of nuclear weapons; Appendix II: Nuclear reactor radiation and its effects; Appendix III: Relative health risks in electricity generation.