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 Wisconsin, the determination of death is governed by state statutes that align with the medical and ethical standards commonly accepted. According to Wisconsin Statute 146.71, a person is legally dead when there is an irreversible cessation of spontaneous respiratory and circulatory functions, or when all functions of the entire brain, including the brain stem, have irreversibly ceased. The statute allows for the use of accepted medical standards to make this determination, which means that a physician's declaration of death is based on the medical criteria of the time. The pronouncement of death itself is a medical action that establishes the fact of death but does not determine the legal cause, manner, or exact time of death. These latter aspects are typically determined through a death investigation, which may involve medical examiners or coroners, depending on the circumstances surrounding the death.