This Safety Guide deals with PSR for an operating nuclear power plant. PSR is a comprehensive safety review of all important aspects of safety@ carried out at regular intervals@ typically every ten years. In addition@ a PSR may be used in support of the decision making process for license renewal or long term operation@ or for restart of a nuclear power plant following a prolonged shutdown. The review process described in this Safety Guide is valid for nuclear power plants of any age and may have a wider applicability@ for example to research reactors and radioactive waste management facilities@ by means of a graded approach. However@ PSR may not be an appropriate means for identifying safety issues in the decommissioning phase@ although the documentation resulting from the PSR of an operating nuclear power plant will be an important input when planning decommissioning.