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 York, the determination of death is governed by the New York Public Health Law, which defines death as either the irreversible cessation of circulatory and respiratory functions or the irreversible cessation of all functions of the entire brain, including the brain stem. This definition aligns with the Uniform Determination of Death Act, which has been adopted in some form by most states. In practice, a licensed physician must make the determination of death based on accepted medical standards. The pronouncement of death is a medical declaration that a person has died, which is distinct from the legal determination of the cause, manner, or time of death. The latter determinations are typically made by a coroner or medical examiner through a death investigation and are documented in a death certificate.