String instruments, stringed instruments, or chordophones are musical instruments that produce sound from vibrating strings when the performer plays or sounds the strings in some manner. There are several types of string instruments: those in which the strings are plucked, hit or struck, or bowed with rosin-coated hair stretched out onto a tensioned musical bow. Plucked string instruments include types which the performer plucks with their fingers, fingernails, or a plectrum (commonly called a “pick”) they are holding, such as the acoustic guitar and other plucked instruments in which the performer presses a key on a keyboard, causing a mechanism to pluck the string or strings (e.g., the harpsichord). String instruments in which the player hits the string include the hammered dulcimer and the piano, although with the piano, the performer presses a key on a keyboard, causing a mechanism to strike the string with a felt hammer. With bowed instruments, the player strokes the strings with a horsehair bow, causing them to vibrate (or, with a hurdy-gurdy, operates a mechanical wheel which strokes the strings).

Bowed instruments include the string section instruments of the Classical music orchestra (violin, viola, cello and double bass) and a number of other instruments (e.g., viols and gambas used in early music from the Baroque music era and fiddles used in many types of folk music). All of the bowed string instruments can also be plucked with the fingers, a technique called “pizzicato”. A wide variety of techniques are used to sound notes on the electric guitar, including plucking with the fingernails or a plectrum, strumming and even “tapping” on the fingerboard and using feedback from a loud, distorted guitar amplifier to produce a sustained sound. Some types of string instrument are mainly plucked, such as the harp and the electric bass. In the Hornbostel-Sachs scheme of musical instrument classification, used in organology, string instruments are called chordophones. Other examples include the sitar, rebab, banjo, mandolin, ukulele, and bouzouki.

In most string instruments, the vibrations are transmitted to the body of the instrument, which often incorporates some sort of hollow or enclosed area. The body of the instrument also vibrates, along with the air inside it. The vibration of the body of the instrument and the enclosed hollow or chamber make the vibration of the string more audible to the performer and audience. The body of most–but not all string instruments–is hollow. There are exceptions, such as types of electric guitar and electric bass which often have a solid wood body; with the electric guitar, a guitar amplifier is used to make the vibrations of the strings audible to the performer and audience.