According to five American playwrights and a director.
‘The Threepenny Opera’ (1928) by Bertolt Brecht and Kurt Weill
“When we think of how music is used in theater, we talk about Rodgers and Hammerstein’s 1943 ‘Oklahoma!,’ which many people feel was the first book musical,” says the playwright David Henry Hwang, 68. “But Brecht’s play, with its jazz-influenced score by Weill, was one of the first to use music as a device to comment on what was happening in the play.”