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 Missouri, a living will is recognized under the Missouri Living Will Declaration Act. This document allows an individual, known as the declarant, to outline their preferences for medical treatment in the event that they are unable to communicate due to a terminal illness or an irreversible condition. The living will can include instructions on whether to administer, withhold, or withdraw life-sustaining treatments. Missouri law requires that the living will be in writing, signed by the declarant, and witnessed by two individuals who are not related to the declarant by blood or marriage and who do not stand to inherit from the declarant. The document does not need to be notarized. In addition to a living will, Missouri residents can also create a Durable Power of Attorney for Health Care, which designates another person to make medical decisions on their behalf if they become incapacitated. It's important for individuals to ensure that their living will and any other advance directives comply with Missouri's specific legal requirements to be valid and enforceable.