Clarinet is the most important woodwind in the orchestra, and has a very wide range. It has 18 holes, six of which are covered by fingers and the remainder by keys. The pitch of the tone is determined by covering the holes.

Clarinets used to all be made of wood but now many are made of ebonite. All have single reeds. There are thirteen different types of clarinets, but the most common in orchestras are the B-flat for the keys with flats and the A for the keys with sharps. Clarinets have a smooth, even sound, which makes them compatible with most orchestral instruments. They can play many different moods, and can play very loud or very soft. Because of this, in military bands a clarinet plays the role of the violin. If an orchestra requires a saxophone, and one is not available, a clarinet could play that role also. The lower-sounding clarinets (like the alto, bass and contrabass) have upturned metal bells, which cause them to resemble a saxophone in appearance. The bass clarinet is comparable to the cello in pitch.