Which instrument in orchestral writing uses the alto clef?

The viola is the instrument in orchestral writing that primarily uses the alto clef. This clef is specifically designed to accommodate the range of pitches that the viola typically plays, placing middle C on the middle line of the staff, which is ideal for the instrument's range. Understanding clefs is essential in orchestral writing, as different instruments are notated in different clefs based on their pitch range and historical convention.

The violin, for example, uses the treble clef, while the cello accepts the bass clef and occasionally the tenor clef for higher passages. The double bass predominantly uses the bass clef, reflecting its lower pitch range. Therefore, the viola's standard use of the alto clef makes it unique among these instruments, solidifying its identity in orchestral music notation.