A power of attorney(POA) or letter 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.

A Power of Attorney can be general, giving the agent the authority to conduct any type of business on behalf of the principal, or specific, and limited to the transactions expressly outlined in the document.