A living will is a legal document that a person uses to make known his or her wishes regarding life prolonging medical treatments. It can also be referred to as an advance directive, health care directive, or a physician's directive. A living will should not be confused with a living trust, which is a mechanism for holding and distributing a person's assets to avoid probate. It is important to have a living will as it informs your health care providers and your family about your desires for medical treatment in the event you are not able to speak for yourself.
Generally, a living will describes certain life prolonging treatments. You, the declarant, indicate which treatments you do or do not want applied to you in the event you either suffer from a terminal illness or are in a permanent vegetative state. A living will does not become effective unless you are incapacitated; until then you'll be able to say what treatments you do or don't want.