A tuning fork is an acoustic resonator in the form of a two-pronged fork with the prongs formed from a U-shaped bar of elastic metal, usually steel. It resonates at a specific constant pitch when set vibrating by striking it against a surface or with an object, and emits a pure musical tone once the high overtones fade out. The pitch of a tuning fork depends on the length and mass of the two prongs. Tuning forks are traditional sources of standard pitch for tuning musical instruments. They are also used in many other applications to produce a fixed tone, such as in medical exams to assess a patients hearing.

Tuning forks produce several tones when struck, but their shape tends to minimize the harmonics, and within a few seconds, only the fundamental can be heard. Longer tines vibrate more slowly and thus produce a lower tone, while shortening the length of the tines allows them to vibrate faster and thus produce a higher sound. The invention of the tuning fork is generally credited to the British musician John Shore in 1711.

Tuning forks have been around for centuries and are the only sure-fire way to tell if an instrument is in tune. They are simple to make and easy to use, and guarantee 100 percent pitch accuracy. Today, electronic tuners have largely replaced tuning forks in tuning musical instruments.