This IAEA publication is the first of its kind to provide comprehensive decision-making assistance for Nuclear Power Plant (NPP) owners and operators. It examines the necessary considerations for effective decision-making: analysing current challenges and opportunities, as well as learning from past events and experiences. It provides practical examples of best practice, efficient tools and frameworks for effective decision-making and discusses the common pitfalls. The guidance found in this publication is equally applicable to other nuclear facilities and installations, such as waste storage and fuel processing plants.