Fervaal, Op. 40, is an opera (action musicale or lyric drama) in three acts with a prologue by the French composer Vincent d'Indy. The composer wrote his own libretto, based in part on the lyric poem Axel[1] by the Swedish author Esaias Tegnér. D'Indy worked on the opera during the years 1889 to 1895,[2] and the score was published in 1895.