Béla Bartók, (born March 25, 1881, Nagyszentmiklós, Hung., Austria-Hungary—died Sept. 26, 1945, New York, N.Y., U.S.), Hungarian composer, pianist, and ethnomusicologist. He was an accomplished pianist at an early age. In 1904 he set about researching Hungarian folk music, having discovered that the folk-music repertory generally accepted as Hungarian was in fact largely urban Roma (Gypsy) music (see Rom).

His fieldwork with the composer Zoltán Kodály formed the basis for all later research in the field, and he published major studies of Hungarian, Romanian, and Slovakian folk music. He worked folk themes and rhythms into his own music, achieving a style that was at once nationalistic and deeply personal. He also toured widely as a virtuoso pianist.

In 1940 he immigrated to the U.S., where he had great difficulty making a living. His works include the opera Bluebeard’s Castle (1911), six celebrated string quartets (1908–39), the didactic piano set Mikrokosmos (1926–39), Sonata for Two Pianos and Percussion (1937), Concerto for Orchestra (1943), and three piano concertos (1926, 1931, 1945).