Carla Bley (born Lovella May Borg, May 11, 1936) is an American jazz composer, pianist, organist and bandleader. An important figure in the free jazz movement of the 1960s, she is perhaps best known for her jazz opera Escalator over the Hill (released as a triple LP set), as well as a book of compositions that have been performed by many other artists, including Gary Burton, Jimmy Giuffre, George Russell, Art Farmer, John Scofield and her ex-husband Paul Bley. Bley was born in Oakland, California, United States, to Emil Borg (1899–1990), a piano teacher and church choirmaster, who encouraged her to sing and to learn to play the piano, and Arline Anderson (1907–1944), who died when Bley was eight years old. After giving up the church to immerse herself in roller skating at the age of fourteen, she moved to New York at seventeen and became a cigarette girl at Birdland, where she met jazz pianist Paul Bley. She toured with him under the name Karen Borg, before she changed her name in 1957 to Carla Borg and married Paul Bley the same year adopting the Bley name. He encouraged her to start composing. The couple later divorced but she kept his surname professionally.

A number of musicians began to record Bley’s compositions: George Russell recorded “Bent Eagle” for his album Stratusphunk in 1960; Jimmy Giuffre recorded “Ictus” on his album Thesis; and Paul Bley’s Barrage consisted entirely of her compositions. Throughout her career, Bley has thought of herself as a writer first, describing herself as 99 percent composer and one percent pianist.