There are two concepts of brain death: death of the entire brain and death of the brainstem. Brain death implies a permanent loss of consciousness and irreversible damage to the functions of the brain and brainstem. Patients with established brain death are potential candidates for organ donation. Determining brain death is primarily based on clinical findings, which in some cases can be supplemented by imaging diagnostic procedures based on clinical guidelines. Clinical confirmation of brain death is based on a physical examination and the determination of the absence of certain clinical signs of brain and brainstem function. Brain death is also confirmed by paraclinical tests that are divided into two main groups: neuroimaging methods that show the absence of cerebrovascular flow and methods that show the absence of cortical electrical activity. In this overview, different concepts of death, epidemiology, etiology, pathophysiology, and diagnostic criteria for determining brain and brainstem death will be presented. The aim of the paper is to point out the key terms related to brain death and its diagnosis. In the coming years, the goal of medicine should be to achieve uniformity in diagnostic criteria for determining brain death throughout the world.