André Charles Prosper Messager (French: [mɛsaʒe]; 30 December 1853 – 24 February 1929) was a French composer, organist, pianist and conductor. His compositions include eight ballets and thirty opéras comiques, opérettes and other stage works, among which his ballet Les Deux Pigeons (1886) and opéra comique Véronique (1898) have had lasting success; Les P'tites Michu (1897) and Monsieur Beaucaire (1919) were also popular internationally.

Messager took up the piano as a small child and later studied composition with, among others, Camille Saint-Saëns and Gabriel Fauré. He became a major figure in the musical life of Paris and later London, both as a conductor and a composer. Many of his Parisian works were also produced in the West End and some on Broadway; the most successful had long runs and numerous international revivals. He wrote two operatic works in English, and his later output included musical comedies for Sacha Guitry and Yvonne Printemps.

As a conductor, Messager held prominent positions in Paris and London, at the head of the Opéra-Comique, the Paris Opéra, the Orchestre de la Société des Concerts du Conservatoire, and the Royal Opera House, Covent Garden. Although as a composer he is known chiefly for his light works, as a conductor he presented a wide range of operas, from Mozart to Richard Strauss, and he acquired a reputation as a conductor of Wagner. In Paris he conducted the world premieres of Debussy's Pelléas et Mélisande, Massenet's Grisélidis and Charpentier's Louise. At Covent Garden, he gave the British premieres of operas by Saint-Saëns and Massenet.

Messager's music became known for its melodic and orchestral invention, musical craftsmanship, and characteristically French elegance and grace. Although most of his works have been infrequently revived, historians of music consider him the last major figure in French opéra comique and opérette.