Agency Definition: A fiduciary relationship between one person (a principal) and another (an agent) that the agent shall act on the principal's behalf. Related Terms: Agent, Principal In Batzel v Smith, Justice Berzon of the United States Court of Appeals adopted these words:"Agency is the fiduciary relationship that arises when one person (a principal) manifests assent to another person (an agent) that the agent shall act on the principal's behalf and subject to the principal's control, and the agent manifests assent or otherwise consents so to act."REFERENCES: Batzel v. Smith, 333 F. 3d 1018 (2003)Duhaime, Lloyd, Agency Law Categories & Topics: Contract Law Dictionary Find you are constantly looking up definitions? Try our search provider (works in most modern browsers) If you find an error or omission in Duhaime's Legal Dictionary, or if you have legal term suggestion, we'd love to hear from you!