Within an agency, agents may specialize. Some agencies only represent actors in one or two fields. Agencies can represent from several to over a 1000 actors, depending on size of agency. All reputable agencies are franchise with the Screen Actors Guild, the actors union, and are regulated by the state. Many agents require actors to sign contracts, usually for a period of one year.
Some agents prefer to keep actors unsigned for a trial period.
Agents are empowered by law to negotiate contracts between performers and employers. Many but not all managers find employment opportunities for their actors above and beyond what an agent can find, and many actors find that the additional commission is well worth it. Managers also advise regarding teachers and coaching, headshots, and general career direction, including selection of agent. A committed manager may find himself coaching his actors at the studio as they prepare to audition.