Rebecca Helferich Clarke (27 August 1886 – 13 October 1979) was a British-American classical composer and violist. Internationally renowned as a viola virtuoso, she also became one of the first female professional orchestral players. Born in England (of a German mother and an American father), Rebecca Clarke claimed both British and American nationalities and spent substantial periods of her long life in the United States, where she permanently settled after World War II. She was born in Harrow and studied at the Royal Academy of Music and Royal College of Music in London. Stranded in the United States at the outbreak of World War II, she married composer and pianist James Friskin in 1944. Clarke died at her home in New York at the age of 93.
Although Clarke's output was not large, her work was recognised for its compositional skill and artistic power. Some of her works have yet to be published (and many were only recently published); those that were published in her lifetime were largely forgotten after she stopped composing. Scholarship and interest in her compositions revived in 1976. The Rebecca Clarke Society was established in 2000 to promote the study and performance of her music.