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 Maine, a living will is referred to as an Advance Health Care Directive (AHCD). The AHCD allows an individual, known as the principal, to outline their preferences for medical treatment in the event that they are unable to communicate their wishes due to a medical emergency. This document can include instructions on the administration, withholding, or withdrawal of life-sustaining treatments if the principal is in a terminal condition or in a state of permanent unconsciousness. Maine's laws regarding AHCDs are found in the Maine Health Care Advance Directive Act, which is part of the Maine Revised Statutes. The Act allows individuals to appoint a health care agent to make decisions on their behalf and to provide specific instructions regarding their health care. Additionally, Maine recognizes Do Not Resuscitate (DNR) orders, which are separate from AHCDs and specifically direct medical personnel not to perform cardiopulmonary resuscitation (CPR) if the patient's breathing or heart stops.