Libretto (pronounced ; plural libretti ), from Italian, is the diminutive of the word libro ("book"). Sometimes other language equivalents are used for libretti in that language, livret for French works and Textbuch for German. A libretto is distinct from a synopsis or scenario of the plot, in that the libretto contains all the words and stage directions, while a synopsis summarizes the plot. Some ballet historians also use the word libretto to refer to the 15–40 page books which were on sale to 19th century ballet audiences in Paris and contained a very detailed description of the ballet's story, scene by scene.
The relationship of the librettist (that is, the writer of a libretto) to the composer in the creation of a musical work has varied over the centuries, as have the sources and the writing techniques employed.
In the context of a modern English language musical theatre piece, the libretto is often referred to as the book of the work, though this usage typically excludes sung lyrics.
Libretti for operas, oratorios and cantatas in the 17th and 18th centuries generally were written by someone other than the composer, often a well-known poet. Metastasio (1698–1782) (real name Pietro Trapassi) was one of the most highly regarded librettists in Europe. His libretti were set many times by many different composers. Another noted 18th-century librettist was Lorenzo Da Ponte, who wrote the libretti for three of Mozart's greatest operas, as well as for many other composers.
Eugène Scribe was one of the most prolific librettists of the 19th century, providing the words for works by Meyerbeer (with whom he had a lasting collaboration), Auber, Bellini, Donizetti, Rossini and Verdi. The French writers' duo Henri Meilhac and Ludovic Halévy wrote a large number of opera and operetta libretti for the likes of Jacques Offenbach, Jules Massenet and Georges Bizet. Arrigo Boito, who wrote libretti for, among others, Giuseppe Verdi and Amilcare Ponchielli, also composed two operas of his own.