The viol is a five-, six-, or seven-string instrument made of wood and most commonly played with a bow, though it may also be plucked or struck. It comes in a variety of sizes, from high treble or pardessus down to contrabass (violone). As its Italian name, viola da gamba, implies, the instrument is customarily held upright between the legs. Common morphological characteristics of instruments in the viol family include a flat back and a slightly curved top. A bridge, usually fairly low and gently arched, supports the strings. The usually thin and wide neck features adjustable frets (typically seven), though other combinations are possible. Instruments related to the viol, such as the baryton or lirone, additionally accommodate a range of sympathetic strings. The belly of the instrument includes a soundhole on either side, often C-shaped, F-shaped (like a violin), or flame-shaped; anomalous sound holes are also present in historical exemplars, as are rosettes or other carved features. According to some early commentators, the viol was the first Western stringed instrument to utilize a soundpost, a feature that contributed to the resonant sound for which the viol family is noted. The origins of what we in the 21st century call the viol are still somewhat obscure; the most commonly accepted narrative places the earliest recognizable iterations of the instrument on the Iberian Peninsula at the end of the 15th century. From there, the viol spread to Italy, where it quickly gained popularity among elites. And thence extends a tradition stretching nearly unbroken until today of an instrument cherished by kings and commoners, children and the elderly, amateurs and professionals alike. Part of the instrument’s appeal lies not just in its comfortable and elegant playing position but in its great musical flexibility. It may be played solo in melodic or polyphonic chordal styles or in consort with other viols, other instruments, or voices. The bass viol—the preeminent soloist of the family—was also a favored continuo instrument, while treble models such as the pardessus or quinton made violin repertoires accessible to new publics. All told, the rich musical possibilities and complex social life of the viol have generated reams of commentary and scholarship. This article primarily focuses on major sources regarding the instrument and its construction; performance practice is only lightly touched upon, and repertoire is largely ignored.