In the years since the landmark Karen Ann Quinlan case, an ethical, legal, and societal consensus supporting patients' rights to refuse life-sustaining treatment has become a cornerstone of bioethics. Patients now legally can write advance directives to govern their treatment decisions at a time of future incapacity, yet in clinical practice their wishes often are ignored. Examining the tension between incompetent patients' prior wishes and their current best interests as well as other challenges to advance directives, the author offers a comprehensive argument for favoring advance instructions during the dying process. He clarifies widespread confusion about the moral and legal weight of advance directives, and he prescribes changes in law, policy, and practice that would not only ensure that directives count in the care of the dying but also would define narrow instances when directives should not be followed. He also presents and develops an original theory of prospective autonomy that recasts and strengthens patient and family control.