The double bass (also known as the contrabass, string bass, upright bass, bull fiddle, bass fiddle, bass violin, or simply bass) is the largest and lowest pitched bowed string instrument used in the modern symphony orchestra. It is a standard member of the string section of the symphony orchestra blank">The Orchestra: A User's Manual, Andrew Hugill with the Philharmonia Orchestra and smaller string ensembles Chamber Music in the Vienna Double Bass Archive, Alfred Planyavsky in _Western classical music. In addition, it is used in other genres such as jazz, 1950s-style blues and rock and roll, rockabilly/psychobilly, bluegrass, and tango.

Double basses are 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 family or from the violin family; while the double bass has features which are similar to those found on violin family instruments, it also has features which may be derived from the viola 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 bowing and plucking styles are used. In jazz music, the bass is mostly plucked, except for some solos which are performed with the bow. In most other genres, such as blues and rockabilly, the bass is plucked.