A power of attorney is a written authorization to represent or act on another's behalf in private affairs, business, or some other legal matter. The person authorizing the other to act is the principal, grantor, or donor of the power. The one authorized to act is the agent, attorney, or in some common law jurisdictions, the attorney-in-fact. Formerly, the term "power" referred to an instrument signed under seal while a "letter" was an instrument under hand, meaning that it was simply signed by the parties, but today a power of attorney does not need to be signed under seal.

Types:

Durable - Under the common law, a power of attorney becomes ineffective if its grantor dies or becomes "incapacitated," meaning unable to grant such a power, because of physical injury or mental illness, for example, unless the grantor (or principal) specifies that the power of attorney will continue to be effective even if the grantor becomes incapacitated. This type of power of attorney is called "power of attorney with durable provisions" in the United States or "enduring power of attorney", "lasting" or "continuing" power of attorney elsewhere. In effect, under a durable power of attorney, the authority of the attorney-in-fact to act and/or make decisions on behalf of the grantor continues until the grantor's death.

Health Care - In some jurisdictions, a durable power of attorney can also be a "health care power of attorney." This particular affidavit gives the attorney-in-fact the authority to make health-care decisions for the grantor, up to and including terminating care and life support. The grantor can typically modify or restrict the powers of the agent to make end-of-life decisions. In many jurisdictions a health care power of attorney is also referred to as a "health care proxy" and, as such, the two terms are sometimes used interchangeably. A living will is a written statement of a person's health care and medical wishes but does not appoint another person to make health care decisions. Depending upon the jurisdiction, a health care power of attorney may or may not appear with an advance health care directive in a single, physical document.

Springing - In some U.S. states and other jurisdictions, it is possible to grant a springing power of attorney,a power that takes effect only after the incapacity of the grantor or some other definite future act or circumstance. After such incapacitation the power is identical to a durable power, but cannot be invoked before the incapacity. This power may be used to allow a spouse or family member to manage the grantor's affairs in case illness or injury makes the grantor unable to act. If a springing power is used, the grantor should specify exactly how and when the power springs into effect. As the result of privacy legislation in the U.S., medical doctors will often not reveal information relating to capacity of the principal unless the power of attorney specifically authorizes them to do so.

Standardized Forms - Standardized forms are available for various kinds of powers of attorney, and many organizations provide them for their clients, customers, patients, employees, or members. However, the grantor should exercise caution when using a standardized POA form obtained from a source other than a lawyer because there is considerable variation in approved formats among the states. In some jurisdictions statutory power of attorney forms are available.

A power of attorney may be: special also called limited, general, or temporary. A special power of attorney is one that is limited to a specified act or type of act. A general power of attorney is one that allows the agent to make all personal and business decisions.A temporary power of attorney is one with a limited time frame.If ever required, a durable power of attorney can be revoked or changed as long as the principal is still mentally competent to act.