In recent decades, the number of IAEA Member States planning to extend the operation of their nuclear power plants (NPPs) beyond the time frame originally anticipated has steadily increased. These decisions have been influenced by the significant economic advantages offered by the long term operation (LTO) of existing NPPs. This Safety Report complements IAEA Safety Standards Series Nos SSR-2/2 (Rev. 1), Safety of Nuclear Power Plants: Commissioning and Operation, and SSG-48, Ageing Management and Development of a Programme for Long Term Operation of Nuclear Power Plants. It provides information on selected topics from the latter, and specifically, it addresses data collection and record keeping, scope setting for structures, systems and components, plant programmes, corrective action programmes, and documentation of ageing management and LTO assessment. The publication focuses on NPPs throughout their lifetime, including operation beyond the time frame originally established for their operation and decommissioning, while considering the different reactor designs that exist around the world. It is also relevant for facilities for spent fuel storage and radioactive waste management at NPPs. It may also be used as a basis for managing the ageing of other nuclear installations and for radioactive waste management facilities. This Safety Report is intended to provide information for operating organizations but may be also used by regulatory bodies.