This technical report, one of a series on the management of ageing nuclear power plants, presents methodologies for selecting plant components important to safety whose ageing should be assessed and for performing ageing management studies. Although the report has been developed for the management of ageing of plant components important to safety, the methodology studies are applicable to components important to plant life. Contents: 1. Introduction; 2. Approach to the management of NPP ageing; 3. Selection of NPP components important to safety for ageing management studies; 4. Methodology for ageing management studies; 5. Recommendations for ageing management pilot studies; Appendix I: Examples of ageing related component degradation and failure; Appendix II: Ageing degradation mechanisms and susceptible materials and components; Appendix III: Examples of summary results of ageing management studies from the USNRC’s Nuclear Plant Ageing Research Programme; Appendix IV: Examples of condition indicator trending as a basis for mitigating component ageing.