The violin is the most important instrument in the orchestra, as well as being a fabulous solo instrument. Two violins form half of a string quartet, with the addition of a viola and a cello.

The violin is an extremely expressive instrument with a brilliant tone, in the hands of a competent player.

The 4 strings from lowest to highest, are tuned at intervals one fifth apart, namely G below middle C, D above middle C, A above middle C, and the E one and a bit octaves above middle C. The range is from the G below middle C (the lowest open string), which is G3 in MIDI notation, up to E7 in MIDI notation, which is the E above the C three octaves above middle C. This is an outstandingly wide range, with a high note way above the highest in most other orchestral instruments.

The violin is generally played with a bow, in the player's right hand, with the violin tucked under the chin, and the player's left hand holds the neck, with the four fingers stopping the 4 strings to create the desired pitch for each note. By continuously gliding the bow back and forth over the string, a violinist can sustain a note as long as he wants.  Alternatively, the strings may be plucked, as with a guitar, producing a short staccato sound called "pizzicato".

The modern orchestra typically uses about 32 violins (some as firsts, some as seconds), which is far more than any other instrument. The sound of massed violins playing in precise synchrony is incredibly beautiful, and quite different from the sound of a single solo violin. The MIDI system tries to achieve the effect of a mass of violins (perhaps with violas and cellos)  by using the Strings sound.