Doubling in the playing of musical instruments can have two different meanings:
- Instrumental doubling may mean that two instruments are playing the same notes together (the players may be playing the same kind of instrument, or they may be playing two different kinds of instrument). It may also refer to singing voices, e.g. "the sopranos are doubled by the clarinet" i.e. the clarinet is playing the same notes that the sopranos are singing.
- Instrumental doubling may mean that one player plays two different instruments in a piece of music (though not at the same time). For example: many people who play the flute also play the piccolo. If an orchestra is playing a piece that needs "two flutes and a third flute doubling piccolo" it means that the third flautist also has a piccolo. Sometimes he or she will need to put the flute down and play the piccolo, then perhaps swap round again.
The term "doubling" is often used in the woodwind section. An oboist may sometimes double on the cor anglais, a clarinettist may sometimes double on a bass clarinet, and a bassoonist may double on a contrabassoon. At other times such instruments may need a separate player. At the beginning of a musical score there should be a list of instruments that makes it clear how many players are needed.