A low-pitched woodwind instrument in the double reed family that plays music written in the bass and tenor clefs, and occasionally the treble. It has a long wooden body attached to a U-shaped lateral tube that leads to the mouthpiece. The bassoon's double reed produces a characteristic nasal quality, 2 octaves lower than the range of the oboe, that lends distinctive colour to the woodwind instruments.

The contrabassoon, or double bassoon, has a range one octave lower than the bassoon. There are also an alto bassoon (also known as an octave bassoon) and a tenor bassoon (or tenoroon), but these are relatively rare.

Developed in the 17th century based on a 16th century instrument called a dulcian, it is the ancestor of the English curtal and French sordone used in the Renaissance. Appearing in its modern form in the 19th century, the bassoon figures prominently in orchestral, concert band and chamber music literature. It is known for its distinctive tone colour, wide range, variety of character and agility.

The modern bassoon exists in two forms: Buffet (or French) and Heckel (or German) system. Most of the world plays the Heckel system, while the Buffet system is primarily played in France, Belgium and parts of Latin America.