The contrabassoon is the lowest-pitched member of the oboe family.
The contrabassoon, also called the double bassoon, is a large double-reed instrument that sounds one octave below the bassoon. Its long conical bore is folded back on itself several times so that the instrument can be held and played by one performer. Because of its size and weight, it normally rests on a floor peg or support.
In orchestral music, the contrabassoon reinforces the lowest bass lines and can add a dark, rough-edged color. It is especially useful for strengthening the bassoon section, low woodwinds, and sometimes the lower strings or brass. Its written music generally uses bass and tenor clefs, with notation conventions varying by passage.
The instrument is not the same as a bassoon, which belongs to the same family but plays an octave higher. Nor is it a contrabass clarinet: that instrument uses a single reed and a mostly cylindrical bore.