A bridge is a device that supports the strings on a stringed musical instrument and transmits the vibration of those strings to another structural component of the instrument—typically a soundboard, such as the top of a guitar or violin—which transfers the sound to the surrounding air. Depending on the instrument, the bridge may be made of carved wood (violin family instruments, acoustic guitars and some jazz guitars), metal (electric guitars such as the Fender Telecaster) or other materials. The bridge supports the strings and holds them over the body of the instrument under tension.

Most stringed instruments produce sound through the application of energy to the strings, which sets them into vibratory motion, creating musical sounds. The strings alone, however, produce only a faint sound because they displace only a small volume of air as they vibrate. Consequently, the sound of the strings alone requires impedance matching to the surrounding air by transmitting their vibrations to a larger surface area that displaces a larger volume of air (and thus produces louder sounds). This calls for an arrangement that lets the strings vibrate freely, but also conducts those vibrations efficiently to the larger surface. A bridge is the customary means for accomplishing this. The bridge conducts the vibrations of the strings to a hollowed out chamber in a number of instruments (e.g., violin family, acoustic guitar, balalaika).

On electric guitars and electric basses, the bridge conducts the vibrations to the body, but the vibrations of the strings are typically sensed by a magnetic pickup, so that an electric signal is created, which is then connected to a guitar amplifier and a speaker enclosure to produce the sound the performer and audience hears. On electric pianos, the player presses or strikes keys, which cause hammers to strike metal tines. A magnetic pickup senses these vibrations, using the same approach as with an electric guitar (amplifier and speaker).

Typically, the bridge is perpendicular to the strings and larger surface (which are roughly parallel to one another) with the tension of the strings pressing down on the bridge and thus on the larger surface beneath it. That larger, more acoustically responsive surface may be coupled to a sound chamber—an enclosure such as the body of a guitar or violin—that provides resonance that helps amplify the sound. Depending on the type of stringed instrument, the resonant surface the bridge rests on may be made of:

Bridges may consist of a single piece of material, most commonly wood for violins and acoustic guitars, that fits between the strings and the resonant surface. Alternatively, a bridge may consist of multiple parts. One common form is a bridge with a separate bearing surface, called a saddle, that supports the strings. This is often of a material harder than the bridge itself, such as bone, ivory, high-density plastic, or metal. Some acoustic guitar bridges have multiple materials, such as a bridge support and "feet" made of wood and a plastic or bone "ridge" where the strings are positioned against.

A classical guitar saddle sits loosely in the hardwood bridge, held in place by string tension. Strings pass through shallow grooves in the saddle, at least for the treble strings, which prevents them moving around during hard playing.

Yet another type of multi-part bridge is common on instruments with a curved sound plate, such as an arch-top guitar or mandolin. Such instruments often have a bridge with a base and separate saddle that can be adjusted for height. On classical and flat-top guitars the bridge is glued to the top. A bridge held on to the top by string tension, as in banjos and archtop jazz guitars, is called a floating bridge, and requires a separate tailpiece to anchor the strings. Electric guitars typically have a metal bridge, often with adjustable intonation screws.

Bridge pins or string pegs are used on some musical instruments to locate the string precisely in the horizontal plane, and in the case of harpsichords to affect the sustain of the strings. They are usually made of steel in modern pianos, of brass in harpsichords, and bone or synthetics on acoustic guitars. Electric guitars do not usually have bridge pins as with acoustic guitars; they are used to transfer the sound from the strings into the hollow body of the instrument as well as holding the strings in place.