The cor anglais, or English horn, is a double-reed woodwind instrument in the oboe family. It is approximately one and a half times the length of an oboe, making it essentially an alto oboe in F.

A double reed is a type of reed used to produce sound in various wind instruments. In contrast with a single reed instrument, where the instrument is played by channeling air against one piece of cane which vibrates against the mouthpiece and creates a sound, a double reed features two pieces of cane vibrating against each other. This means, for instruments with the double reed fully exposed, that the air flow can be controlled by the embouchure from the top, bottom and sides of the reed. The term double reeds can also refer collectively to the class of instruments which use double reeds.