mandolin (Italianmandolino; literally 'small mandola') is a musical instrument in the lute family and is usually plucked with a plectrum or 'pick'. It commonly has four courses of doubled strings tuned in unison, although five and six course versions also exist. The courses are normally tuned in a succession of perfect fifths. It is the soprano member of a family that includes the mandola, octave mandolinmandocello, and mandobass. It descends from the mandore.

There are many styles of mandolin, but three are common, the Neapolitan or round-backed mandolin, the carved-topmandolin and the flat-backed mandolin. The carved-top or arch-top mandolin has a much shallower, arched back, and an arched top—both carved out of wood. The flat-backed mandolin uses thin sheets of wood for the body, braced on the inside for strength in a similar manner to a guitar. Each style of instrument has its own sound quality and is associated with particular forms of music. Neapolitan mandolins feature prominently in European classical music and traditional music. Carved-top instruments are common in American folk music and bluegrass music. Flat-backed instruments are commonly used in Irish, British and Brazilian folk music. Some modern Brazilian instruments feature an extra fifth course tuned a fifth lower than the standard fourth course.

Other mandolin varieties differ primarily in the strings, and include MilaneseLombardBrescian, and other six-course types (tuned in fourths), as well as four-string models (one string per course), and the Sicilian twelve-string (three strings per course) model. There have also been made instruments with sixteen-strings (four strings per course).