The cello is a bowed string instrument with four strings tuned in perfect fifths. It is a member of the violin family of music instruments, which also includes the violin, viola and the contrabass.

The word derives from the Italian 'violoncello'. The word derives ultimately from vitula, meaning a stringed instrument. 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.

Cellos were derived from other mid-to-large sized bowed instruments in the 16th century, such as the viola da gamba, and the generally smaller and squarer viola da braccio, and such instruments were made by members of the Amati family of luthiers. The invention of wire-wrapped strings in Bologna gave the cello greater versatility. By the 18th century the cello had largely replaced other mid-sized bowed instruments.