When Bela Bartok died in September of 1945, he left a partially completed viola concerto commissioned by the virtuoso violist William Primrose. Yet, while no definitive version of the work exists, this concerto has become arguably the most-performed viola concerto in the world. The story of how the concerto came to be, from its commissioning by Primrose to its first performance to the several completions that are performed today is told here in Bartok's Viola Concerto: The Remarkable Story of His Swansong.