Arrigo Boito (Italian: [arrio bito]; 24 February 1842 10 June 1918) (whose original name was Enrico Giuseppe Giovanni Boito and who wrote essays under the anagrammatic pseudonym of Tobia Gorrio) was an Italian poet, journalist, novelist, librettist and composer, best known today for his libretti, especially those for Giuseppe Verdi's last two monumental operas Otello and Falstaff (not to mention Amilcare Ponchielli's operatic masterpiece La Gioconda) and his own opera Mefistofele. Along with Emilio Praga and his own brother Camillo Boito, he is regarded as one of the prominent representatives of the Scapigliatura artistic movement.

Mefistofele (Italian pronunciation: [mefiˈstɔːfele]) is an opera in a prologue and five acts, later reduced to four acts and an epilogue, the only completed opera with music by the Italian composer-librettist Arrigo Boito (there are several completed operas for which he was librettist only). The opera was given its premiere on 5 March 1868 at La Scala, Milan, under the baton of the composer, despite his lack of experience and skill as a conductor.

However, it was not a success and was immediately withdrawn after only two performances. Revisions in 1875 resulted in success in Bologna and, with further adjustments in 1876 for Venice, the opera was performed elsewhere.