A libretto is a work containing the words associated with a musical performance such as an opera, operetta, or musical. It includes the lyrics to the songs as well as any spoken passages. The relationship of the libretto to the development of the musical work varies. Some composers, notably Richard Wagner, would write the libretto as well as the music. Others would adapt the libretto from an existing play, or have this done for them, as with Francesco Maria Piave, who adapted works by Victor Hugo, the Duke of Rivas, and others. Still others used works specifically written for the purpose of being turned into opera, such as the libretti of Lorenzo da Ponte and Hugo von Hofmannsthal.
Many writers of libretti have been sadly overlooked in the receipt of credit for their work. Certainly some were recognized as part of famous collaborations, as with Gilbert and Sullivan. However, in many other cases the composer of the musical score to an opera or operetta has been given the lion's share of credit for the completed work, and the writer of the lyrics relegated to a mere footnote.