A string quartet consists of two violins, a viola, and a cello. The term "string quartet" also refers to a piece written for such a group. Since the middle of the Classical Period, it has generally been the most popular genre of chamber music for both composers and audiences alike.
With a few exceptions, almost every major composer throughout history has written music for the string quartet. The most notable among them include (but are not limited to!) Haydn, Beethoven, Brahms, Bartók, and Shostakovich, to name only a small handful.
Because of the huge size of the string quartet repertoire, many
members of professional string quartets usually don't have much
room in their schedules to include teaching or solo careers.
Besides performing at concerts and recitals, quartets often play at
weddings, receptions, and other fancy get-togethers.