A living will -- also known as an advance medical directive -- is a statement of your wishes for the kind of life-sustaining medical intervention you want (and don't want) in the event that you become terminally ill and unable to communicate.

Most states have living will statutes that define when a living will goes into effect (for example, when a person has less than six months to live). And state law may restrict the medical interventions to which such directives apply.

Your condition and the terms of your directive also will be subject to interpretation. Different institutions and doctors may come to different conclusions. As a result, in some instances a living will may not be followed. But patients' wishes are taken very seriously, and an advance medical directive is one of the best ways to have a say in your medical care when you can't express yourself otherwise.

You increase your chances of enforcing your directive when you have a health-care agent advocating on your behalf.

You can name such an agent by way of a health-care proxy, or by assigning what's called a medical power of attorney. You sign a legal document in which you name someone you trust to make medical decisions on your behalf in the event that you can't do so for yourself.

A health-care proxy applies to all instances when you're incapacitated, not just if you're terminally ill.

Choose your health-care agent carefully. That person should be able to do three key things: understand important medical information regarding your treatment, handle the stress of making tough decisions, and keep your best interests and wishes in mind when making those decisions.