The cello ( /ˈtʃɛloʊ/ chel-oh; plural cellos or celli) is a bowed string instrument with four strings tuned in perfect fifths. It is a member of the violin family of musical instruments, which also includes the violin, viola, and double bass. Old forms of the instrument in the Baroque era are baryton and viol (viola da gamba).

A person who plays a cello is called a cellist. The cello is used as a solo instrument, in chamber music, in a string orchestra and as a member of the string section of an orchestra. It is the second largest bowed string instrument in the modern symphony orchestra, the double bass being the largest.