The double bass, also called the string bass, upright bass, bass violin or contrabass, is the largest and lowest-pitched bowed string instrument in the modern symphony orchestra. The name "double bass" derives from the early use of the instrument to double—an octave lower where possible—the bass part written for the cello. The double bass is a standard member of the string section of the symphony orchestra^[1] and smaller string ensembles^[2] in Western classical music. In addition, it is used in other genres such as disco, jazz, 1950s-style blues and rock and roll, rockabilly/psychobilly, traditional country music, bluegrass, and tango.

The double bass is typically constructed from several types of wood, including maple for the back, spruce for the top, and ebony for the fingerboard. It is uncertain whether the instrument is a descendant of the viola da gamba or or the violin, but it is traditionally aligned with the violin family. While the double bass is nearly identical in construction to other violin family instruments, it also embodies features found in the older viol family.

Like many other string instruments, the double bass is played either with a bow (arco) or by plucking the strings (pizzicato). In orchestral repertoire and tango music, both arco and pizzicato are employed. In jazz, pizzicato is the norm, except for some solos and also occasional written parts in modern jazz that call for bowing. In most other genres, such as blues and rockabilly, the bass is plucked.