The previous two articles in this series explored the historical and theoretical development of medical decision making from initial reliance on medical beneficence to a more recent emphasis on patient autonomy. The law of withholding and withdrawal of treatment has much in common with medical ethics. It is based on concerns about patient autonomy expressed by courts, legislatures, and the executive branch of the government. Legally, the patient’s right of self-determination has been based on a variety of sources ranging from state and federal constitutions to the common law of torts and from cases to statutes and regulations. Understanding the various sources of the law, the distinctions among those sources, and the interaction of the branches of government in this context assists in understanding the law itself. In our federalist system of government, significant legal variations can exist among the states, but although technically valid, excessive concern about compliance with the precise contours of each state’s statute when surrogate decision makers are engaging in bedside deliberations is unnecessary. Regardless of source or precise legal contours, the overall goal, which neither the physician nor the patient’s surrogate or proxy decision makers should forget, is to honor what the patient would want to have done. Physicians and attorneys will agree on that as a matter of both ethics and the law.