What instruments make up a standard string quartet?

A standard string quartet consists of four instruments: two violins, one viola, and one cello.12

This ensemble has been the predominant genre of chamber music since approximately 1750. While the term "quartet" can refer to any group of four performers or musical parts, it is most commonly associated with this specific string configuration. In a mature string quartet, the composition typically features equal participation among all four instruments, following the formal principles of the sonata.12