A power of attorney gives one or more persons, called your “agent,” the authority to act on your behalf and may be limited to a particular activity or be all-encompassing. The power may take effect immediately or upon the occurrence of a future event, usually one that determines you are no longer able to act for yourself due to a mental or physical disability. A power of attorney can be revoked, but usually you would have to provide a written statement of the revocation to the person named your agent.