[en] This Safety Guide provides detailed guidance on the provisions of the Code on the Safety in Nuclear Power Plants: Operation, IAEA Safety Series No. 50-C-O(Rev.1) on the maintenance of structures, systems and components. Like the Code, the Guide forms part of the IAEA's programme, referred to as the NUSS programme, for establishing Codes and Safety Guides relating to nuclear power plants. Effective maintenance is essential for safe operation of a nuclear power plant. It not only ensures that the level of reliability and effectiveness of all plant structures, systems and components having a bearing on safety remains in accordance with design assumptions and intent, but also that the safety status of the plant is not adversely affected after commencement of operation. Nuclear power plant maintenance requires special attention because of: Limitations set by requirements that a minimum number of components remain operable even when the plant is shut down in order to ensure that all necessary safety functions are guaranteed; Difficulty of access to some plant items even when the plant is shut down, due to radiation protection constraints; Potential radiological hazards to site personnel and the public. This Guide covers the organizational and procedural aspects of maintenance but does not give detailed technical advice on the maintenance of particular plant items. It gives guidance on preventive and remedial measures necessary to ensure that all structures, systems and components important to safety are capable of performing as intended. The Guide covers the organizational and administrative requirements for establishing and implementing preventive maintenance schedules, repairing defective plant items, selecting and training maintenance personnel, providing maintenance facilities and equipment, procuring stores and spare parts, reviewing, controlling and carrying out plant modifications, and generating, collecting and retaining maintenance records for establishing and implementing an adequate maintenance feedback information system