libretto (ləbrĕt´ō) [Ital.,=little book], the text of an opera or an oratorio. Although a play usually emphasizes an integrated plot, a libretto is most often a loose plot connecting a series of episodes. Characterization and emotion are suggested by the words of a libretto but are expressed by the music. The first major librettist was Ottavio Rinuccini, an Italian poet of the 16th cent. Outstanding in the 17th cent. was Philippe Quinault, and in the 18th cent. important librettists were the poet Pietro Metastasio, many of whose 50 libretti were set numerous times by major composers, Ranieri di Calzabigi, and Lorenzo Da Ponte. The 19th-century librettists of note included Augustin Eugène Scribe, W. S. Gilbert, and the composers Arrigo Boito and Richard Wagner; prominent in the 20th cent. was Hugo von Hofmannsthal.