The determination and pronouncement of when a person has died has medical, ethical, and legal implications. Laws vary from state to state, and death is usually defined in a state’s statutes.

Definitions and terminology may vary from state to state but generally a person is dead when, according to ordinary standards of medical practice, there is irreversible cessation of the person's spontaneous respiratory and circulatory functions. If artificial means of support preclude a determination that a person's spontaneous respiratory and circulatory functions have ceased, the person is dead when, in the announced opinion of a physician, according to ordinary standards of medical practice, there is irreversible cessation of all spontaneous brain function.

Death occurs when the relevant functions cease. But a formal pronouncement of death is not a legal determination of the cause, manner, or time of death.

In New Jersey, the determination of death is governed by the New Jersey Declaration of Death Act. According to this act, an individual is considered dead when there is an irreversible cessation of all circulatory and respiratory functions, or when there is an irreversible cessation of all functions of the entire brain, including the brain stem, according to ordinary standards of medical practice. The determination must be made by a licensed physician. The use of artificial means of support may necessitate the application of brain death criteria to determine death. The pronouncement of death itself is a medical determination, and it is distinct from the legal determination of the cause, manner, or time of death, which may be subject to further investigation or certification by a medical examiner or coroner.