Agency law is concerned with any "principal"-"agent" relationship; a relationship in which one person has legal authority to act for another. Agency is an agreement, express , or implied, by which one of the parties, called the principal, entrusts to the other, called the agent, the management of some business; to be transacted in his name, or on his account, and by which the agent assumes to do the business and to render an account of it. As a general rule, whatever a man may do by himself, except by virtue of a delegated authority, he may do by an agent.