In tragic plays of Ancient Greece, the chorus (choros) is believed to have grown out of the Greek dithyrambs and tragikon drama. The chorus offered background and summary information to help the audience follow the performance, commented on main themes, and showed how an ideal audience might react to the drama as it was presented. They also represent the general populace of any particular story. The chorus usually communicated in song form, but sometimes the message was spoken. It was the playwright's job to choreograph the chorus.

In early tragedy, all parts were played by a single actor; because the actor left the stage often to change roles, the chorus was especially dominant. It is thought to have numbered approximately 50 singing and dancing members (choreutai) circa 508. Tragedy came to be composed of episodes separated by choral odes. In these odes, the chorus would chant rhythmically, so they could be viewed as one entity rather than individuals. In the second generation of Athenian tragedy the chorus often had a more substantial role in the narrative; in Euripedes's The Bacchae, for example, the chorus, representing the frenzied female worshippers of Dionysus becomes a central character in itself.

Aeschylus reduced the chorus to 12 members, but it remained critical to his productions. Under Aeschylus, the chorus played such key roles as the protagonist in The Suppliants, and the antagonist in The Eumenides. Sophocles increased the chorus to 15 members, although the choral odes became only tenuously related to the dramatic action. The Sophoclean chorus was divided into two sub-choruses of 6 (hemichoria) and a leader (koryphaios); the number of actors increased from two to three. The leader of the chorus interacted with the characters in the play, and spoke for the general population (the play's public opinion). This change favoured the interaction between actors and thus brought ancient Greek tragedy closer to the modern notion of dramatic plot. The size of the tragic chorus continued to waver, settling for a time at 3 members.

Use of the chorus can be seen not only in Ancient Greek tragedies, but also in more recent works such as Shakespeare's Romeo and Juliet and the film Little Shop of Horrors

Ancient Greek theatre

Coro grieco | Chœur (théâtre) | Coro greco | Chór (teatr antyczny) | Khoros