The term string quartet refers to either a type of musical composition or a group of four people who play them. Many composers from the mid-18th century onwards wrote string quartets. The associated musical ensemble consists of two violinists, a violist, and a cellist. The double bass is almost never used in the ensemble mainly because it would sound too loud and heavy.

The violin, colloquially known as a fiddle, is a wooden chordophone, and is the smallest, and thus highest-pitched instrument (soprano) in regular use in the violin family. Smaller violin-type instruments exist, including the violino piccolo and the pochette, but these are virtually unused. Most violins have a hollow wooden body, and commonly have four strings, usually tuned in perfect fifths with notes G3, D4, A4, E5, and are most commonly played by drawing a bow across the strings. The violin can also be played by plucking the strings with the fingers (pizzicato) and, in specialized cases, by striking the strings with the wooden side of the bow.