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 Connecticut, the determination of death is governed by state statutes that align with the medical and ethical standards commonly accepted. According to Connecticut law, 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. This definition is consistent with the Uniform Determination of Death Act, which has been adopted in some form by most states. The pronouncement of death must be made by a licensed physician according to ordinary medical standards. It is important to note that the pronouncement of death itself does not establish the legal cause, manner, or exact time of death; these are separate determinations that may be made later, often as part of a death certificate's completion or during an autopsy or inquest, if applicable.