Bellini followed up the success of his tender comedy La Sonnambula with this grand and exotic tale. In its keen characterization and its dramatic conflict between love and patriotic duty it anticipates the major themes of several Verdi operas. The conflict in the opera is between the native Druids of Britain and the Roman soldiers who are occupying the country. The Druid leaders are Oroveso (the High Priest) and Norma (the High Priestess), and the main Romans are the Proconsul Pollione and his centurion Flavio. Norma was Vincenzo Bellini's eighth opera and the one that completely secured his fame and fortune as a composer. Although, according to some contemporary reviews, the audience responded coolly to some aspects of Norma at its first performance at Milan's La Scala opera house on December 26, 1831, the public soon warmed to it and made it a popular success. In the nineteenth century, musicians as diverse as Richard Wagner, Giuseppe Verdi, Johannes Brahms, and Gustav Mahler, regarded Norma as a pivotal work. Today Norma is accepted as Bellini's most successful tragic opera.
Felice Romani based the libretto on Alexandre Soumet's play of the same name, which had premiered in Paris in April 1831 to great critical acclaim. In 1998, David Kimbell noted that, despite this immediate literary source, the opera's plot and the nature of its title character have an earlier source in the Greek myth of Medea. Kimbell has also noted the distinct similarities between Romani's Norma and his text for Giovanni Pacini's opera La sacerdotessa d'Irminsul (1820).
The music of Norma is laden with all of the conventions of Italian opera in the first half of the nineteenth century, including solo vocal arias and duets, some of which follow the prototypical Rossinian crescendo into full-fledged end-of-act choruses. After the introduction, Pollione's cavatina ("Meco all'altar di Venere") foreshadows the events of the opera. Its form is essentially ternary, with the C minor tonality, nervous violin tremolo, and rhythmically active lower strings of the B section contrasting with the C major tonality of the A section. But Bellini avoids a complete reprise of the A section, returning ultimately to the disturbing minor-mode inflections and nervous instrumental texture of the B material. Pollione's cavatina is paired with a cabaletta ("Me protegge, mi defende"), in which he sings of the protective power of love, in the heroic key of E flat major and triumphant dotted rhythms. Norma's famed cavatina, "Casta diva," a prayer to the moon goddess, is introduced by a silvery flute solo over undulating violin arpeggios. Rather than independently, as previously in "Va crudele, al Dio spietato"/"E tu pure, ah! tu non sai!," Pollione and Adalgisa together in their duet "Vieni in Roma"/"Ciel! Così parlar l'ascolto sempre" complete musical phrases: once Adalgisa agrees to go to Rome with Pollione, she is under his musical control. A similar concept governs the Act II duet between Adalgisa and Norma ("Mira, o Norma"/"Ah! perchè la mia costanza"), in which Norma's weakening resolve to allow Adalgisa to beg for Pollione's return is mirrored in her willingness to adopt Adalgisa's musical language. The finale of Act I consists of a trio in which Norma is musically pitted against Pollione and Adalgisa, and in that of Act II, Oroveso and the chorus of druids punctuate Norma's central aria ("Deh! Non voleri vittime") as she ascends her funeral pyre.