Agency is an area of commercial law dealing with a contractual or quasi-contractual tripartite set of relationships when an Agent is authorized to act on behalf of another (called the Principal) to create a legal relationship with a Third Party.[1] Succinctly, it may be referred to as the relationship between a principal and an agent whereby the principal, expressly or impliedly, authorizes the agent to work under his control and on his behalf. The agent is, thus, required to negotiate on behalf of the principal or bring him and third parties into contractual relationship. 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.