Oh, What a Lovely War! is an epic musical developed by Joan Littlewood and her ensemble at the Theatre Workshop in 1963. It is a satire on World War I, and by extension on war in general. The title is derived from the "somewhat satirical" music hall song "Oh! It's a Lovely War!", which is one of the major numbers in the production.

Joan Maud Littlewood was an English theatre director who trained at the Royal Academy of Dramatic Art, and is best known for her work in developing the Theatre Workshop. She has been called "The Mother of Modern Theatre". Her production of Oh, What a Lovely War! in 1963 was one of her more influential pieces.