A string (or stringed) instrument is one that produces sound by means of vibrating strings.

The most common stringed instruments in Western music are those in the violin and guitar families (stringed keboard instruments such as the piano are classified separately).

Stringed instruments are usually categorised by the technique used to produce sound. In order for a stringed instrument to produce sound, its string or strings must vibrate, which can be achieved in several ways:

- plucked - using the finger or thumb or some form of plectrum (e.g. guitar)

- bowed - by drawing a bow across the strings (e.g. cello)

- struck - using a hammer (e.g. dulcimer)

Other methods can include air movement (e.g. aeolian harp), turning a wheel (e.g. hurdy gurdy) and magnetic fields (e.g. e-bow).

A vibrating string on its own makes only a very quiet sound, so stringed instruments are usually constructed in such a way that this sound is coupled to a hollow resonating chamber or soundboard. On the violin, for example, the taut strings pass over a bridge resting on a hollow box. The strings' vibrations are distributed via the bridge and soundpost to all surfaces of the instrument and are thus made louder. Technically speaking, no amplification occurs, since all of the energy to produce sound comes from the vibrating string. What really happens is that the soundboard of the instrument provides a larger surface area to create sound waves than that of the string. A larger vibrating surface moves more air, hence produces a louder sound.

Most stringed instruments can be fitted with piezoelectric or magnetic pickups to convert the string's vibrations into an electrical signal which is amplified and then converted back into sound by loudspeakers.