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 Mexico, the determination of death is guided by the Uniform Determination of Death Act (UDDA), which has been adopted by the state. According to New Mexico statutes, a person is legally declared 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, as determined by a physician. The use of artificial means of support may make it difficult to determine if these functions have ceased, but death can still be pronounced when a physician, adhering to accepted medical standards, determines that brain function has irreversibly ceased. The formal pronouncement of death by a physician does not, however, establish the legal cause, manner, or exact time of death; these are separate determinations that may require further investigation or legal proceedings.