<P> The opera libretto from its inception (ca . 1600) was written in verse, and this continued well into the 19th century, although genres of musical theatre with spoken dialogue have typically alternated verse in the musical numbers with spoken prose . Since the late 19th century some opera composers have written music to prose or free verse libretti . Much of the recitative of George Gershwin's opera Porgy and Bess, for instance, is merely DuBose and Dorothy Heyward's play Porgy set to music as written--in prose--with the lyrics of the arias, duets, trios and choruses written in verse . </P> <P> The libretto of a musical, on the other hand, is almost always written in prose (except for the song lyrics). The libretto of a musical, if the musical is adapted from a play (or even a novel), may even borrow their source's original dialogue liberally--much as Oklahoma! used dialogue from Lynn Riggs's Green Grow the Lilacs, Carousel used dialogue from Ferenc Molnár's Liliom, My Fair Lady took most of its dialogue word - for - word from George Bernard Shaw's Pygmalion, Man of La Mancha was adapted from the 1959 television play I, Don Quixote, which supplied most of the dialogue, and the 1954 musical version of Peter Pan used J.M. Barrie's dialogue . Even the musical Show Boat, which is greatly different from the Edna Ferber novel from which it was adapted, uses some of Ferber's original dialogue, notably during the miscegenation scene . And Lionel Bart's Oliver! uses chunks of dialogue from Charles Dickens's novel Oliver Twist, although it bills itself as a "free adaptation" of the novel . </P> <P> As the originating language of opera, Italian dominated that genre in Europe (except in France) well through the 18th century, and even into the next century in Russia, for example, when the Italian opera troupe in Saint Petersburg was challenged by the emerging native Russian repertory . Significant exceptions before 1800 can be found in Purcell's works, German opera of Hamburg during the Baroque, ballad opera and Singspiel of the 18th century, etc . </P> <P> Just as with literature and song, the libretto has its share of problems and challenges with translation . In the past (and even today), foreign musical stage works with spoken dialogue, especially comedies, were sometimes performed with the sung portions in the original language and the spoken dialogue in the vernacular . The effects of leaving lyrics untranslated depend on the piece . </P>

A libretto written by the librettist is the script for the