A letter of attorney, also known as a power of attorney letter, is a legal document that grants one person the authority to act on behalf of another person in certain financial or legal matters. The person granting the authority is called the principal, and the person receiving the authority is called the attorney-in-fact or agent.

For example, a person might grant a power of attorney to their spouse, allowing them to make financial decisions and sign legal documents on their behalf in the event that they become incapacitated or are unable to handle their own affairs. This can include managing bank accounts, paying bills, and making investments.

A letter of attorney can also be used in business transactions. For instance, a company may grant a power of attorney to its attorney-in-fact to negotiate contracts, sign agreements, and handle other legal matters on behalf of the company.