Déjanire is an opera in 4 acts composed by Camille Saint-Saëns to a libretto in French by Louis Gallet and Camille Saint-Saëns. The last of Saint-Saëns' operas, it premiered on 28 August 1898 in the new arènes in Beziers. One of the opera's central characters, Hercule (Hercules), had been the subject of two earlier symphonic poems by Saint-Saëns – Le Rouet d'Omphale (1872) and La Jeunesse d'Hercule (1877). The story is based on The Trachiniae by Sophocles.

Louis Gallet was a French writer of operatic libretti, plays, romances, memoirs, pamphlets, and innumerable articles, who is remembered above all for his adaptations of fiction —and Scripture— to provide librettos of cantatas and opera, notably by composers Georges Bizet, Camille Saint-Saëns and Jules Massenet.