The purpose of this Safety Guide is to provide recommendations and guidance on the conduct of a periodic safety review (PSR) for an existing nuclear power plant. A PSR is a comprehensive safety review of all important aspects of safety, carried out at regular intervals, typically of ten years. The Safety Guide is directed at plant operating organizations and regulatory bodies. The review process described in this Safety Guide is valid for nuclear power plants of any age, but may have a wider applicability, for example, to research reactors and radioactive waste management facilities.