This publication compiles a broad range of experiences and practices related to long term operation (LTO) of Nuclear Power Plants from 18 IAEA Member States. Its primary objective is to support nuclear power plants that are preparing to operate beyond their original licence term or design life. It also offers valuable guidance for organizations seeking to acquire or develop the tools needed to implement effective ageing management in future plants, including those currently in the design or construction phases with LTO considerations. More than 50 experts from around the world have contributed to this publication.