mandolin, musical instrument of the lute family, with a half-pear-shaped body, a fretted neck, and a variable number of strings, plucked with the fingers or with a plectrum. The earlier mandolin, with five double strings, was developed from the mandola, a 17th-century lute. The Neapolitan mandolin, a smaller type having four pairs of strings, became popular in the 18th cent. and is the usual present-day mandolin. In popular music it is generally played with a tremolo motion. Notable uses of the mandolin in serious music are in Mozart's Don Giovanni and in pieces by Beethoven and Mahler.