The viola looks similar to a violin, but it is pitched a perfect 5th below the violin. Held by the performer under the chin just like a violin, the body of the viola is a bit longer and wider than that of the violin. A comparison between the physical sizes of the violin and viola can be seen in the image above. Even though the viola shares three common strings with the violin, the resonance and timbral quality of those strings is significantly distinct from the violin due to the larger size of the instrument.

The viola is the only modern instrument whose music is written almost entirely in the alto clef. In high passages, the violist may also read the treble clef, but the viola is never written in bass or tenor clefs. Natural harmonics up to the 4th harmonic (5th partical) are displayed, but natural harmonics become easier on larger instruments. For this reason, works written for professional players may go up to the 9th or 10th partials. For younger musicians, it is wise to not go beyond the 6th partial.

The bow used by the viola is also slightly larger than a violin bow. It is heavier, which makes it a good choice for rhythmic gestures. The larger bow also can allow for more pronounced accents and other articulations. Regardless of its size, it can match the bowings with both the violin and cello.

The low C string is often described using terms such as "dark" and "rich." The sound of a viola has a covered thick sound quality in its lower range, a quality that lends the instrument to excel at smooth accompaniments. The higher register is strong and intense. The viola often doubles the violins at the octave or in unison, reinforcing melodies in the lower violin register. Unfortunately all too often, the viola section is seen as an overlooked "step child" in the orchestra. Traditionally, the viola section is assigned to play sustained inner harmonic parts, accompaniment figures that serve to fill out harmonies, and other unimaginative gestures. This is due primarily to the range of the viola and its close relationship to the violin; however, the viola is also an extraordinarily expressive instrument that can also do nearly everything else the violin can do.