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 Massachusetts, the determination of death is governed by the legal standards set forth in the state's statutes. The definition of death typically aligns with the medical consensus that a person is considered dead when there is an irreversible cessation of all spontaneous respiratory and circulatory functions. In cases where artificial life support is involved, death is determined when a physician, adhering to ordinary medical standards, declares that there is an irreversible cessation of all brain functions. It is important to note that while the pronouncement of death establishes that a person has died, it does not legally ascertain the cause, manner, or specific time of death. These aspects are usually determined through a separate legal process, such as an autopsy or death investigation, depending on the circumstances surrounding the death.