The chapter deals with the dependability and the functional safety of a system by illustrating the key points of the theoretical corpuses formulated on the two subjects: the dependability theory and the functional safety standards. Dependability is concerned with the ability of a system to deliver the intended service, including the ability to cope with a fault. Functional safety is concerned with the safety-critical systems and focuses on the characteristics of the extra systems added to a system with the purpose of making its operation safe. The chapter starts by providing the definitions of system and service. Then it passes to the illustration of the key concepts of the dependability theory, which are the threats, the attributes, and the techniques used to enforce the dependability. Particular attention is given to the fault-tolerance techniques and the architectures of the faulttolerant systems. Afterwards, the chapter presents the key issues of the functional safety standards, which are the analyses of hazard and risk of a safety-critical system, and the safety requirements for the extra systems. At last, a case of study is examined from the standpoints of both the dependability and the functional safety