Brain death is the complete and irreversible cessation of function of the entire brain, including the brainstem, regardless of the presence or absence of spinal cord and cardiac function. Alternatively, brain death is defined as the widespread, permanent loss of total brain cell function involving the cerebrum, cerebellum, pontine brain, and medulla oblongata. In other words, after the occurrence of total brain death, although the heartbeat is still present, brain resuscitation is no longer possible and individual death has occurred and is inevitable. Brain death is divided into primary brain death and secondary brain death. Primary brain death is caused by primary brain disease or injury; secondary brain death is caused by primary disease or injury of extracerebral organs such as heart and lungs, resulting in brain hypoxia or metabolic disorders. The basic causes of brain death are: severe injury to brain tissue, hemorrhage, inflammation, tumor, cerebral edema, cerebral compression, brain herniation, or secondary to cardiopulmonary dysfunction. Brain death was proposed as a marker of clinical death in the United States in 1966. In 1968, at the 22nd World Medical Congress, the Special Committee on the Review of the Definition of Brain Death at Harvard Medical School proposed “irreversible loss of brain function” as a new criterion for death and established the world’s first diagnostic criteria for brain death: 1. irreversible deep coma; 2. spontaneous respiratory arrest; 3. loss of brainstem reflexes; 4. Loss of brainstem reflexes; 4. Loss of brain waves (flattening). Where the above criteria are met, and repeatedly tested within 24 or 72 hours, with no change in the results, death can be declared. However, two cases of hypothermia (<32.2°C) or having just taken barbiturates and other central nervous system depressants need to be excluded. Since then, many countries have developed diagnostic criteria, but different countries and scholars have different views on the definition of brain death: some scholars in the UK believe that life is determined by the respiratory and circulatory centers, so the irreversible cessation of brainstem function is brain death; the Nordic countries believe that it is the irreversible cessation of brain circulation that causes brain death, so they call brain death a total brain infarction. The latest criteria of the drafting group of the brain death law of our Ministry of Health (Chinese Medical Association, 1999, draft) are: deep coma, total loss of brainstem reflexes, no voluntary breathing (maintained by ventilator, positive apnea test), dilated or fixed pupils, and disappearance of brain waves. Brain death is confirmed only after 12 hours of observation without change after the first diagnosis. Brain death criteria is not only a medical issue, but also an ethical one. It involves not only the patient himself, but also his family's agreement on the criteria for brain death. The Chinese tradition defines death by cardiac arrest and cessation of voluntary breathing. Generally, when brain death is determined, death must be determined by an authoritative physician and with the consent of the family, or if the family does not agree, then it is still defined by the criteria of cardiac death. Second, the establishment of brain death criteria is not directly related to organ transplantation. This point must be made clear. However, objectively, the brain death criteria will have a great promotion effect on organ transplantation utilization.