The Harold is an improvisational long-form. Developed by Del Close and brought to fruition through Close's collaboration with Charna Halpern , Harold has become the signature form of Chicago's ImprovOlympic and is now performed by improvisational comedy troupes and teams across the world.

In its basic form (defined in the book "Truth in Comedy" as the "training wheels Harold" or "competition Harold") Harold is much like a standard television sitcom. It consists of three acts, each comprised of improvised games and scenes. This basic form begins with an opening game, which explores a suggestion provided by the audience. A set of three scenes, usually unrelated to each other, follows the opening game, and is known as the first beat. The actors will then play a game or scene together, known as a group game. The second beat -- another set of three scenes that are inspired somehow by the scenes from the first beat -- follows, and is capped with a second group game. The final set of three scenes (the third beat) combines themes, characters, situations and games from the whole piece and, hopefully, makes surprising and funny connections or intersections among them. Del Close allowed for and encouraged much variation within the structure of the Harold and saw it as a much more malleable and organic form with which to explore themes and ideas.

Harold is a very versatile performance piece: beats and games need not appear in the order or number described above. Harold is the Ur text of longform improvisation, having inspired Harold-related forms as Sybil (one-person Harold), the Movie Form, the Deconstruction, the Bat (an audio-only Harold in the dark) and many others.