The power of the agent to bind the principal is usually legally referred to as authority.
Agency created via an agreement may be a form of implied authority, such as when a person gives their credit card to a close relative, the cardholder may be required to pay for purchases made by the relative with their credit card.
An example of the existence of an agency agreement at issue in a 2006 court case arose when a tennis tournament sponsor sued Venus and Serena Williams for not participating.
The sponsor argued that their father, Richard Williams, had committed to their participation in the tournament.
Within the European Union, there is legislation designed to give some protection to agents, in particular the right to compensation in certain circumstances when an agency is terminated.