Death has been analysed in a heterogeneous way, according to the theological, philosophical and scientific concepts of the world. Until recently death was diagnosed following the cessation of the functions of the heart and lungs. Currently, the ability to maintain cerebral function with mechanical support, in the absence of spontaneous breathing and heart beat, and the power to ensure circulation and respiration, despite the complete destruction of the brain, demand a redefinition of death. There is now the concept of brain death. In this paper we discuss the concept of death, from ancient times to the modem criteria for brain death. The historical definition will be discussed, and the new criteria for diagnosing brain death will be explained.