The double bass (or contrabass) is the lowest-pitched string instrument in the standard orchestra. Among the 'regular' bowed string instruments, it is the only one that is tuned in fourths instead of fifths, with its strings tuned to E1, A1, D2 and G2. It is a transposing instrument, most commonly notated in bass clef, one octave higher than it sounds. Most professional contrabass players use instruments with a 'C extension'. This is basically an extra measure of fingerboard mounted on the head of the instrument, which makes the lowest string capable of reaching a C1 (often present in orchestral works).
The double bassis not only an orchestral instrument: it features in chamber music and solo music, as well as in many popular genres, such as jazz, tango, rock, blues, etc. The double bass can be played with a bow or pizzicato-style. Though orchestral and academic-influenced music in general can demand both techniques, genres such as jazz, blues, and rock double bass lines are played almost exclusively in pizzicato.