The viola is a string instrument that is bowed or played with varying techniques. It is slightly larger than a violin and has a lower and deeper sound. Since the 18th century, it has been the middle or alto voice of the violin family, between the violin and the cello.

It is built in proportions similar to those of the violin but has a body length of 37 to 43 cm (14.5 to 17 inches), about 5 cm (2 inches) longer than a violin. Its four strings are tuned c–g–d′–a′, beginning with the C below middle C. The viola’s tone is darker, weightier, and warmer than that of the violin.