The viola (/viˈoʊlə/) is a bowed string instrument. It is slightly larger than a violin in size and has a lower and deeper sound than a violin. Since the 18th century it has been the middle voice of the violin family, between the violin (which is tuned aperfect fifth above it) and the cello (which is tuned an octave below it).
Music that is written for the viola differs from that of most other instruments, in that it primarily uses the alto clef, which is otherwise rarely used. Viola music employs the treble clef when there are substantial sections of music written in a higher register.
The viola occasionally has a major role in orchestral music. In the earlier part of the 20th century, more composers began to write for the viola, encouraged by the emergence of specialized soloists such as Lionel Tertis. Englishmen Arthur Bliss, York Bowen, Benjamin Dale, and Ralph Vaughan Williams all wrote chamber and concert works for Tertis. William Walton,Bohuslav Martinů and Béla Bartók wrote well-known viola concertos. Paul Hindemith wrote a substantial amount of music for viola. In the latter part of the 20th century a substantial repertoire was produced for the viola.