In the performing arts industry such as theatre, film, or television, casting, or a casting call, is a pre-production process for selecting a certain type of actor, dancer, singer, or extra to land the role of a character in a script, screenplay, or teleplay. This process may be used for a motion picture, television program, documentary film, music video, play, or advertisement intended for an audience.

Actors are selected to play various types of roles. A main cast comprises several actors whose appearances are significant in film, theatre, or television. Their roles are often called starring roles. Within a main cast, there is often a male or female lead who plays the largest role, that of the protagonist in a production. When there is no singular lead, the main roles are referred to collectively as an ensemble cast, which comprises several principal actors and performers who are typically assigned roughly equal screen time. A supporting actor is one with a role that is important to a play or film, but less so than that of the leading actors. A supporting role is more important than a bit part, which involves direct interaction with the principal actors but no more than five lines of dialogue, often referred to as a "five-or-less" or "under-five" in the United States, or "under-sixes" in British television. When a well-known actor or other celebrity appears in a bit part, it is sometimes called a cameo appearance.^{[citation needed]}

The casting process involves a series of auditions before a casting panel, composed of individuals within a production. Usually, in nearly all areas of show business, a casting director is on this panel, and depending on the type of production it may include a theatrical producer and theater director, a television producer, a film producer and film director, or choreographer. In the early stages of this process performers often may present or are presented with prepared audition pieces such as monologues, songs, choreography, scripts or sides.

These audition pieces are usually videotaped, typically in the form of screen tests and then attached with resumes and head shots, then shared with producers, directors, or studio executives. Later stages may involve groups of actors—both union (SAG-AFTRA) and non-union, depending on the size and scope of the production—attempting to read material from the work under consideration, paired up with other actors. With each actor's overall motivational choices evaluated, the casting panel considers both the individual actors and the chemistry created from combinations of them participating in a read-through.^{[citation needed]}

Casting calls may go out into the general public at large, sometimes referred to as a "cattle call" (a U.S. term), or open audition, in which hundreds or even thousands of performers compete for a number of roles.

Casting character breakdowns, not to be confused with script breakdowns, are often provided by production agents who submit their clients to casting, which provides a brief summary of character (age, gender, race or ethnicity, situations they may be involved in).

Well-known actors or actresses have an advantage when it comes to landing roles. An actor may go through several casting calls before receiving a part, and even though well-known actors or actresses often still go through this very necessary process, some are privileged enough to have well-known writers, screenwriters, directors or producers pitch a project for their intent to be cast in a role. By the time some casting directors finish reading a script they may already have ideas about which actors might be right for the roles. Casting directors know that these actors and actresses can bring in big audiences, enhance audience engagement, and bring in high revenue, making these movies a success.

For major productions, the process of selecting actors for sometimes hundreds of speaking parts and roles often requires specialized staff. While the final decision remains with those in charge — such as the director, producer, artistic departments, and the overall production team — a casting director (or CD) is responsible for most of the day-to-day work involved in this process during pre-production. A casting director is often assisted by a casting associate; productions with large numbers of extras may also employ an extras casting director. In the production budget, casting personnel are considered part of the above-the-line staff and typically answer to the director.