Voice-overs are a disembodied voice which is used as a tool in radio, film, theatre, and advertising. There are a number of functions for a voice-over, from educational narration to a vehicle for plot information. In some cases, a voice-over is provided by an established character from the performance, and in other instances it is performed by a specialized actor who focuses his or her career on making voice-overs. Many people are familiar with the basic concept of a voice-over, since it is such a common device in performance media.

Often, a voice-over is used to provide narration. Many educational films provide an off-screen narrator who explains what is going on or provides interesting facts. This allows viewers to focus on the events on screen without being distracted by a visible actor. Commercials also use this technique, with a voice-over extolling the product being advertised while its myriad delights are displayed on the screen.

As a plot device, a voice-over can be used in several ways. In some instances, it is provided by a third party narrator, as in the case of the Stage Manager in Thornton Wilder's Our Town. The narrator provides information and commentary on what is going on without being directly involved, thus establishing basic facts for members of the audience. A voice-over may also be voiced by a character, who may provide commentary on scenes which he or she is in, in addition to discussing events which he or she is not present for. The tactic of asides and comments directed at the audience is very old. Shakespeare, for example, regularly included commentary from his characters which was intended for the audience.

Some styles of film and radio are heavily associated with voice-overs. In film noir, for example, narration by either a major character or a third party is extremely common, as seen in countless films which open with a gravely voice painting a dire picture. Many educational programs use voice-overs to convey information as well. Animated films also use the technique to give their characters voices.

A specialized voice actor can sometimes become quite famous, as is the case with the announcer on many American movie previews. Although most people don't know his name, which happens to be Don LaFontaine, his voice is instantly familiar. Other mainstream actors may agree to guest star as voice actors, as often happens in animated films with voice casts who are better known for their on-screen work.