The balalaika (Russian: балала́йка, pronounced [bəɫɐˈɫajkə]) is a Russian stringed musical instrument with a characteristic triangular wooden, hollow body, fretted neck and three strings. Two strings are usually tuned to the same note and the third string is a perfect fourth higher. The higher-pitched balalaikas are used to play melodies and chords. The instrument generally has a short sustain, necessitating rapid strumming or plucking when it is used to play melodies. Balalaikas are often used for Russian folk music and dancing.

The balalaika family of instruments includes instruments of various sizes, from the highest-pitched to the lowest: the piccolo balalaika, prima balalaika, secunda balalaika, alto balalaika, bass balalaika, and contrabass balalaika. There are balalaika orchestras which consist solely of different balalaikas; these ensembles typically play Classical music that has been arranged for balalaikas. The prima balalaika is the most common; the piccolo is rare. There have also been descant and tenor balalaikas, but these are considered obsolete. All have three-sided bodies; spruce, evergreen, or fir tops; and backs made of three to nine wooden sections (usually maple).

The prima balalaika, secunda and alto are played either with the fingers or a plectrum (pick), depending on the music being played, and the bass and contrabass (equipped with extension legs that rest on the floor) are played with leather plectra. The rare piccolo instrument is usually played with a pick.