György Ligeti composed his Viola Sonata between 1991 and 1994. It is a sonata for viola solo in six movements, and Ligeti composed it in various phases, parallel with his Violin Concerto, and his piano études. The composer was inspired to write a viola sonata after hearing Tabea Zimmermann playing on the radio, then began writing various movements. The second movement Loop, was premiered by Garth Knox, while Facsar was premiered in 1993 by Jürg Dahler. The two movements were conceived as part of a complete work and they became the second and third movements of Ligeti's Viola Sonata.

György Sándor Ligeti was a Hungarian-Austrian composer of contemporary classical music. He has been described as "one of the most important avant-garde composers in the latter half of the twentieth century" and "one of the most innovative and influential among progressive figures of his time".