A living will is not a last will and testament, as they are two different things. A living will is, in reality, quite similar in intent to a power of attorney, rather than a will. The idea behind a living will is to allow the person drafting the document to outline the decisions they have made relating to life support and to direct others, such a medical professionals, about those wishes.
Living wills are more common today that ever before, because medicine has many ways to prolong and sustain a life, even if that person may not recover from a coma. Those who do not wish to live like that can state their desires in a living will. Those who do wish to remain in a coma may also state those wishes.
The living will also covers what the person wishes in terms of life-prolonging medical or surgical care and whether they, and other medications and life support, should be continued or stopped. This is a document that gives voice to what a person wants if they become incapacitated. Living wills may be revoked.
The living will is only valid if the correct forms for the state of residence are used and the will is executed according to the laws of that state. Some states need two witnesses to a signature or the form needs to be signed in the presence of a notary, or both.