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, sometimes against the wishes of the other. The person authorizing the other to act is the principal, grantor, or donor (of the power). The one authorized to act is the agent or, in some common law jurisdictions, the attorney-in-fact (attorney for short). Formerly, a power referred to an instrument under seal while a letter was an instrument under hand, but today both are signed by the grantor, and therefore there is no difference between the two.

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, sometimes against the wishes of the other. The person authorizing the other to act is the principal, grantor, or donor (of the power). The one authorized to act is the agent or, in some common law jurisdictions, the attorney-in-fact (attorney for short). Formerly, a power referred to an instrument under seal while a letter was an instrument under hand, but today both are signed by the grantor, and therefore there is no difference between the two.