Bowing (Italian: Arco) is a method used in some string instruments, including the violin, viola, cello, and the double bass (of the violin family) and the old viol family. The bow consists of a stick with many hairs stretched between its ends. Bowing the instrument's string causes a stick-slip phenomenon to occur, which makes the string vibrate.

The characteristic long, sustained, and singing sound produced by the violin, viola, violoncello, and double bass is due to the drawing of the bow against their strings. This sustaining of musical sound with a bow is comparable to a singer using breath to sustain sounds and sing long, smooth, or legato melodies. Without the bow the violin family could only be played pizzicato.

In modern practice, the bow is almost always held in the right hand while the left is used for fingering. When the player pulls the bow across the strings (such that the frog moves away from the instrument), it is called a downbow; pushing the bow so the frog moves toward the instrument is an upbow (the directions "down" and "up" are literally descriptive for violins and violas, and are employed in analogous fashion for the cello and double bass). Two consecutive notes played in the same bow direction are referred to as a hooked bow; a downbow following a whole downbow is called a retake.

Generally, the downbow stroke is used for the strong musical beats, the upbow for weak beats. However, in the viola da gamba, it is the reverse; thus violinists, violists, and cellists look like they are "pulling" on the strong beats when they play, whereas gamba players look like they are "stabbing" on the strong beats. The difference almost certainly results from the different ways in which the bow is held in these instrument families: violin/viola/cello players hold the wood part of the bow closer to the palm, whereas gamba players use the opposite orientation, with the horsehair closer. The orientation appropriate to each instrument family permits the stronger wrist muscles (flexors) to reinforce the strong beat.

String players control their tone quality by touching the bow to the strings at varying distances from the bridge, emphasizing the higher harmonics by playing sul ponticello "on the bridge," or reducing them, and emphasizing the fundamental frequency by playing sul tasto "on the fingerboard".

Occasionally, composers ask the player to use the bow by touching the strings with the wood rather than the hair; this is known by the Italian phrase col legno, "with the wood". Coll'arco, "with the bow", is the indication to use the bow hair to create the sound in the normal way.

Rarely, the guitar can be played with a bow (rather than plucked) for unique effects.