An eight-string guitar is a guitar with eight strings, or one more than the Russian guitar's seven. Eight-string guitars are less common than six- and seven-string guitars, but they are used by a few classical, jazz, and metal guitarists. The eight-string guitar allows a wider tonal range, or non-standard tunings, or both.

The guitar is a stringed musical instrument that is usually fretted and typically has six or twelve strings. It is usually held flat against the player's body and played by strumming or plucking the strings with the dominant hand, while simultaneously pressing selected strings against frets with the fingers of the opposite hand. A guitar pick may also be used to strike the strings. The sound of the guitar is projected either acoustically, by means of a resonant hollow chamber on the guitar, or amplified by an electronic pickup and an amplifier.