Samuel Osborne Barber (March 9, 1910 – January 23, 1981) was an American composer of classical music best known for his "Adagio for Strings."

He was born in West Chester, Pennsylvania and began to compose at the age of seven.

He studied at the Curtis Institute of Music in Philadelphia before becoming a fellow of the American Academy in Rome in 1935. The following year he wrote his String Quartet in B minor, the second movement of which he would arrange for string orchestra as "Adagio for Strings."

He avoided the experimentalism of some other American composers of his generation, preferring relatively traditional harmonies and forms. His work is lushly melodic and has often been described as neo-romantic.

His songs, accompanied by piano or orchestra, are among the most popular 20th century songs in the classical repertoire. They include a setting of Matthew Arnold's "Dover Beach," originally written for string quartet and baritone, the Hermit Songs on anonymous Irish texts of the 8th to 13th centuries, and , written for the soprano Eleanor Steber and based on an autobiographical text by James Agee, the introductory portion of his novel A Death in the Family. Barber possessed a good baritone voice and, for a while, considered becoming a professional singer. He did make a few recordings, including his own Dover Beach.

Barber's Piano Sonata (1949), a piece commissioned by Richard Rodgers and Irving Berlin, was first performed by Vladimir Horowitz. It was the first large-scale American piano work to be premiered by such an internationally renowned pianist.

Barber also composed several operas. Vanessa, composed to a libretto by Gian Carlo Menotti, premiered at the Metropolitan Opera in New York City. It was a critical and popular success, and Barber won a Pulitzer Prize for it. At the European premiere it met with a chillier reception, however, and is now little played there, although it remains popular in America.

Barber produced three concertos for solo instruments and orchestra, one for violin, one for cello, and one for piano. The New York Philharmonic commissioned an oboe concerto, but Barber was unable to complete it before his death.

Although never a prolific composer, Barber wrote much less after the flop of his opera Antony and Cleopatra (with a libretto by film and opera director Franco Zeffirelli) in 1966.

He died in New York City in 1981.