The subject of brain death usually becomes clinically relevant during a tremendously stressful time. For most practitioners, the need to make a diagnosis of brain death occurs infrequently. Since the introduction of the concept of brain death, the criteria have been refined to their current state. The historical background and the current standards and guidelines used to diagnose brain death will be reviewed. Potential future changes in brain death criteria when contemplating organ donation in the critically ill patient will be discussed.