The textbook begins with a brief chapter discussing the role of nuclear energy in sustainable development in a broader yet crucial context. Going further through the individual chapters, readers become familiar with the fundamental aspects of the safety and security of nuclear installations, including the historical development of issues related to the peaceful use of nuclear power. The reliability theory in engineering systems is addressed in general terms but with concrete examples related to nuclear safety controls. The safety of nuclear power plants is explained via a defense-indepth approach using multi-barrier systems. Consequently, probability risk analysis in nuclear is addressed to provide a better understanding of the current status of nuclear safety and future goals in this regard. A rather large section of the book is devoted to selected nuclear accidents. Following this chapter, students will be able to explain the causes and consequences of major nuclear accidents as well as the lessons learned from these unfortunate milestones in nuclear energy. This chapter is followed by the last chapter about safety culture and the human factor as they are understood today in terms of the safety and reliability of nuclear installations.