His first wife, Marta Ziegler, and second wife, Ditta Pasztory, were both his piano pupils. He never taught composition, fearing that to do so might endanger his own creative work.

Important Bartók works composed between 1907 and 1922 include the opera Bluebeard's Castle (1911), the First and Second String Quartets (1909, 1918), the ballet The Wooden Prince (1914-1916), the two Violin and Piano Sonatas (1921-1922), and the pantomime The Miraculous Mandarin (1918-1919).

After World War I Bartók intensified his career as a concert pianist. He gave the first performances of his first two Piano Concertos (1927, 1930-1931). In 1927 he made his first United States tour, performing a number of his own works to mixed critical reception. Significant compositions include the Two Rhapsodies for violin and piano (1928), the Fourth and Fifth String Quartets (1928, 1934), the Cantata profana (1930), and the earliest books of Mikrokosmos, which is a series of 153 progressive pieces for piano on which Bartók worked from 1926 to 1939.

Bartók's artistic intent at this point in his career is excellently summarized in his essay "The Influence of Peasant Music on Modern Music" (1931). He describes the various ways in which folk music can be transmuted into contemporary art music. In the simplest form the folk melody may be taken over unchanged or only slightly varied, with the addition of an accompaniment and perhaps some opening and closing phrases. The additional material may be merely ornamental in nature, or it may be of primary importance. The next logical step is for the composer to invent his own imitation of a folk melody, then to treat it exactly like the borrowed tune. To Bartók it made no difference whether the composer invented his own themes or borrowed material. He stated emphatically that the composer "has a right to use musical material from all sources. What he has judged suitable for his purpose has become through the very use his mental property…. The question of origins can only be interesting from the point of view of musical documentation."

The highest form of folk-influenced music, Bartok believed, is that in which the folk atmosphere has been completely assimilated. He described such music as follows: "Neither peasant music nor imitations of peasant melodies can be found in his [the composer's] music, but it is pervaded by the atmosphere of peasant music. In this case we may say he has completely absorbed the idiom of peasant music which has become his musical mother tongue." No better description could be given of the part played by folk music in Bartók's mature work.

The political situation of Hungary became more and more unsettled in the mid-1930s. During this period Bartók produced important works: Music for Strings, Percussion, and Celesta (1936); Sonata for Two Pianos and Percussion (1937); Contrasts for violin, clarinet, and piano (1938); the Violin Concerto (1937-1938); and the Sixth String Quartet (1939). When Nazi Germany annexed Austria in 1938, he realized he would have to leave Hungary soon. After the death of his mother in 1939 his last tie was broken.

The following year Bartak and his wife settled in New York City. He was given a temporary appointment at Columbia University, transcribing the records of Serbo-Croatian folk songs in the Parry Collection, which lasted through 1942. Bartók's persistent ill health and resultant inability to perform publicly or to take another position left his financial situation precarious. Fortunately he received important commissions, and assistance from the American Society of Composers, Authors, and Publishers. The Concerto for Orchestra (1943) was commissioned by Serge Koussevitzky; the solo Violin Sonata (1944) by Yehudi Menuhin; and the Viola Concerto (1945) by William Primrose. The last-named work remained unfinished; it was completed by Tibor Serly, one of Bartók's pupils. Bartók worked on his Third Piano Concerto, which he composed for his wife, until a few days before his death. The last 17 measures were still incomplete when he died of leukemia on Sept. 26, 1945.

Bartók's works have steadily risen in popularity since his death. The Concerto For Orchestra, Music for Strings, Percussion, and Celesta, and Sonata for Two Pianos and Percussion have been widely performed and recorded; the six String Quartets belong to the classic repertory of 20th-century chamber music; and Mikrokosmos is considered standard piano-teaching material.

The standard biography of Bartók in English is Halsey Stevens, The Life and Music of Béla Bartók (1953; rev. ed. 1964). An excellent collection of essays from Tempo magazine, including selections from Bartók's writings, is Béla BartóA Memorial Review (1950). Agatha Fassett, The Naked Face of Genius: Béla Bartók's American Years (1958), gives a moving account of Bartók's last years. Bence Szabolcsi, Béla Bartók, His Life in Pictures (1956; trans. 1964), is a good pictorial biography.