Agency is an area of Commercial law dealing with a contractual or quasi-contractual tripartite set of relationships when an Agent is authorised to act on behalf of another (called the Principal) to create a legal relationship with a Third Party. This branch of law separates and regulates the relationships between:

• Agents and Principals;
• Agents and the Third Parties with whom they deal on their Principals' behalf; and
• Principals and the Third Parties when the Agents purport to deal on their behalf.

The common law principle in operation is usually represented in the Latin phrase, qui facit per alium, facit per se, i.e. the one who acts through another, acts in his or her own interests and it is a parallel concept to vicarious liability and strict liability in which one person is held liable in Criminal Law or Tort for the acts or omissions of another..