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 Hampshire, the determination of death is guided by state statutes that align with the general medical and legal standards for defining death. According to New Hampshire law, a person is considered legally dead when there is an irreversible cessation of circulatory and respiratory functions, or when there is an irreversible cessation of all functions of the entire brain, including the brain stem. This determination must be made in accordance with accepted medical standards. The use of artificial means of support may necessitate a brain-based determination of death if it prevents the assessment of respiratory and circulatory function. The pronouncement of death is a medical judgment made by a physician and is distinct from the legal determination of the cause, manner, or time of death, which may be subject to further investigation or certification by medical examiners or coroners.