A periodic safety review is considered an effective way to obtain an overview of nuclear power plant safety. It is also used to determine reasonable and practicable modifications to maintain a high level of safety during continued operation, and to justify operation of a nuclear power plant beyond the original time frame. The review considers life limiting processes and features of structures, systems and components important to safety, and whether there are any foreseeable circumstances that could endanger the safe operation of the nuclear power plant. This publication addresses the scope of assessment, methods and applicable criteria within the periodic safety review and long term operation programmes framework, to support decision making for long term operation of nuclear power plants.