A living will—also known as an Advance Health Care Directive—is a document in which the declarant or principal (person making the living will) specifies what kind of medical treatment the declarant does and does not want if the declarant has a medical emergency and is unable to communicate those wishes. A living will may direct health care providers to administer, withhold, or withdraw life-sustaining treatments if the declarant is in a terminal or irreversible condition.

Laws and terminology for documents related to living wills, Advance Health Care Directives, Do Not Resuscitate orders (DNRs), and other health care documents vary from state to state. These laws are generally located in a state’s statutes—often in the probate code or estates code.

In Massachusetts, living wills are not explicitly recognized by statute, but the state does recognize health care proxies, which are similar to Advance Health Care Directives. Under Massachusetts law, specifically Massachusetts General Laws Chapter 201D, an individual may appoint a health care agent through a health care proxy to make medical decisions on their behalf if they become incapacitated and unable to make or communicate their own decisions. The health care agent is authorized to make decisions about the individual's medical treatment, including decisions to refuse or withdraw life-sustaining treatment. While living wills are not statutorily recognized, they can still be useful as they may provide guidance to the health care agent and physicians regarding the individual's preferences for treatment in end-of-life situations. It is important for individuals to discuss their wishes with their health care agent and ensure that their health care proxy is consistent with their treatment preferences. Do Not Resuscitate orders (DNRs) are separate documents that instruct medical personnel not to perform cardiopulmonary resuscitation (CPR) if a person's breathing or heartbeat stops. In Massachusetts, DNR orders are typically part of a patient's medical record and are signed by a physician.