As an instrumentalist Bowen considered the tone quality of the viola to be superior to the violin, and composed numerous works for viola. Bowen frequently performed as a pianist alongside the viola player Lionel Tertis and in 1908 Tertis premiered Bowen's Viola Concerto in C minor, Op. 25. Bowen also aided Tertis in his campaign to increase the popularity of the viola as a solo instrument. Bowen made numerous other contributions to the viola repertoire, including the "Fantasy Quartet" for four violas and two sonatas for viola and piano. Alongside Arnold Bax and Benjamin Dale, Bowen was one of the first English composers to add original works to the modern viola repertoire. Bowen also wrote three traditional string quartets, the second (of 1918) published in 1922 as part of the Carnegie Collection of British Music, and a "Phantasy Quintet" for string quartet and bass clarinet in 1932.