The number of keys differs between the six types of clarinets. The A clarinet and B-flat clarinet are the standard types of clarinets, and most have 17 or 18 keys.
The B-flat clarinet is the most frequently used clarinet in wind orchestras and jazz ensembles. The A clarinet is not used in jazz, but it is still widely used in classical music. In many musical pieces, one musician may play both the B-flat and A clarinets. Minor design variations exist in modern clarinets, which partially accounts for the different number of keys. The other types of clarinets are E-flat, alto, bass and contra clarinets.