Arrigo Boito (February 24, 1842 – June 10, 1918) was an Italian poet, novelist and composer, best known today for his opera libretti and his own opera, Mefistofele.

Born in Padua, Boito studied music at the Milan Conservatoire. The premiere of his only finished opera, Mefistofele, based on Goethe's Faust, came in 1868. The premiere was badly received, provoking riots and duels over its supposed "Wagnerism", and it was closed by the police after two performances. But Boito's revised and drastically cut version (which also changed Faust from a baritone to a tenor) was a great success, and it is still frequently performed and recorded today. Other than this work, Boito wrote very little music, completing but later destroying another opera, Ero e Leandro, and leaving a further opera, Nerone, incomplete at his death. Excluding the last act, for which he left only a few sketches, it was finished by Arturo Toscanini and Vincenzo Tommasini and premiered at Il Teatro alla Scala in 1924. Mefistofele is the only work of his performed with any regularity today.

As well as writing the libretti for his own operas, Boito wrote them for other composers, the most notable examples being for Giuseppe Verdi's Falstaff and Otello, and (as "Tobia Gorrio") for Amilcare Ponchielli's La Gioconda.

Boito was director of the Parma Conservatoire from 1889 to 1897. He died in Milan and was interred there in the Cimitero Monumentale.