A variety of mechanical vibrato systems for guitar have been developed since the 1930s. They are used to add vibrato to the sound by changing the tension of the strings, typically at the bridge or tailpiece of an electric guitar using a controlling lever (often referred to as a whammy bar, vibrato arm/bar, or tremolo arm/bar). The lever enables the player to quickly vary the tension and sometimes the length of the strings temporarily, changing the pitch to create a vibrato, portamento or pitch bend effect.

Instruments without this device have other bridge and tailpiece systems. The mechanical vibrato systems began as a device for more easily producing the vibrato effects that blues and jazz guitarists had long produced on arch top guitars by manipulating the tailpiece with their picking hand. However, it has also made many sounds possible that could not be produced by the old technique, such as the 1980s-era shred guitar "dive bombing" effect.