A power of attorney is an instrument containing an authorization for one to act as the agent of the principal that terminates at some point in the future either by its terms or by operation of law such as death of the principal or agent.  They are also called letters of attorney.  The person appointed is usually called an Attorney-in-Fact.  A power of attorney which does not provide for a successor attorney-in-fact to be appointed will terminate at the death of the attorney-in-fact.  The person making the power of attorney appointment is called the principal.  A power of attorney can be general, durable or limited.  Some states have adopted a statutory power of attorney.  Other specific types of power of attorneys include: Health Care Power of Attorney, Power of Attorney for Care and Custody of Children, Power of Attorney for Real Estate matters and Power of Attorney for the Sale of a Motor Vehicle. Power of attorney requirements vary by state, but typically are signed by the principal and need to be witnessed and notarized.

Law relating to power of attorney varies from state to state.  The laws of some of the states relating to power of attorney can be found at the following links.