A mandolin is a musical instrument which is plucked, strummed or a combination of both. It is descended from the mandora. The most common design as originated in Naples, Italy has eight metal strings in four pairs (courses) which are plucked with a plectrum. Variants include four-string (one string per course), six-string (one string per course) as per the Milanese design, twelve-string (three strings per course), and sixteen-string (four string per course). It has a body with a teardrop-shaped soundtable (i.e. face), or one which is essentially oval in shape, with a soundhole, or soundholes, of varying shapes which are open and not latticed.
A mandolin's typically hollow wooden body has a neck with a flat (or slightly radiused) fretted fingerboard, a nut and floating bridge, a tailpiece or pinblock at the edge of the face to which the strings are attached, and mechanical tuning machines, rather than friction pegs, to accommodate metal strings. Like the guitar, the mandolin has relatively poor sustain; that is, the sound from a plucked string decays quickly. A note cannot be maintained for an arbitrary length of time as with a bowed note on a violin. Its small size and higher pitch makes this problem more severe than with the guitar, and the use of tremolo (rapid picking of one or more pairs of strings) is often used to create a sustained note or chords. This technique works particularly well with a mandolin's paired strings, where one of the pair is sounding while the other is being struck by the pick, giving a more rounded and continuous sound than is possible with a single coursed instrument.
Mandolins come in several forms. The Neapolitan style, known as a round-back or bowl-back (or "tater-bug", colloquial American) has a vaulted back made of a number of strips of wood in a bowl formation, similar to a lute, and usually a canted, two-plane, uncarved top. The Portuguese bandolim, a flat-back style, is derived from the cittern, but is tuned the same as most mandolins. Another form has a banjo-style body.
At the very end of the nineteenth century, a new style, with a carved top and back construction inspired by violin family instruments began to supplant the European-style bowl-back instruments, especially in the United States. This new style is credited to mandolins designed and built by Orville Gibson, a Kalamazoo, Michigan luthier who founded the "Gibson Mandolin-Guitar Manufacturing Co., Limited" in 1902. Gibson mandolins evolved into two basic styles: the Florentine or F-style, which has a decorative scroll near the neck, two points on the lower body, and usually a scroll carved into the headstock; and the A-style, which is pear shaped, has no points, and usually has a simpler headstock.
These styles generally have either two f-shaped soundholes like a violin (F-5 and A-5), or an oval sound hole (F-4 and A-4 and lower models) directly under the strings. Much variation exists between makers working from these archetypes, and other variants have become increasingly common. The Gibson F-hole F-5-style mandolins have come to be considered the most typical and traditional for playing American bluegrass music, while the A-style is generally more associated with Irish, folk, or classical music. The more complicated woodwork also translates into a more expensive instrument.
Internal bracing in the F-style mandolins was usually achieved with parallel tone bars, similar to a violin's bassbar. Some makers instead employ "x-bracing" which is simply two tone bars mortised to each other to cross into an X supporting the top. Some luthiers are now using a "modified x-bracing", which incorporates both a tone bar and x-bracing.
Numerous modern mandolin makers build instruments which are largely replicas of the Gibson F-5 Artist models built in the early 1920s by Gibson acoustician Lloyd Loar. Original Loar-signed instruments are sought after and extremely valuable.
Other American-made variants include the Howe-Orme guitar-shaped mandolin (manufactured by the Elias Howe Company between 1897 and roughly 1920), which featured a cylindrical bulge along the top from fingerboard end to tailpiece, and the Vega mando-lute (more commonly called a cylinder-back mandolin manufactured by the Vega Company between 1913 and roughly 1927), which had a similar longitudinal bulge but on the back rather than the front of the instrument.
As with almost every other contemporary string instrument, another modern variant is the electric mandolin. These mandolins can have four (single), five (single) or eight (double) strings.