French horn, brass wind musical instrument. Fundamentally a metal tube of narrow conical bore, it is curved into circles because of its great length. The horn ends in a wide flare. It is a development (c.1650) of the small hunting horn. Although sometimes used in a more grandiose manner, it is still employed symphonically to produce the simple woodland sound. In modern orchestras it is usually in the key of F and is a transposing instrument. The present-day French horns normally have three valves, introduced in the 19th cent. The valves supplanted crooks that were used in the 18th cent. to reduce the horn to different keys. Hand stopping and modulation are still used to control the open tone, though mutes may also be used. The first important work to call for valved horns was Halévy's opera La Juive.

Orchestral and military brass instrument, a valved circular horn with a wide bell. It is normally a transposing instrument (its music written in a different tone than its actual sound) in F. It has a wide bore and three (sometimes four) rotary valves; its conical mouthpiece produces a mellower tone than the cup-shaped mouthpieces of other brass instruments. Horns long relied on separable crooks—circular lengths of tubing that could be attached and removed rapidly—for music modulating to new keys. Since circa 1900 the standard horn has been a “double” instrument, with built-in crooks in F and B-flat that can be selected rapidly by means of a thumb valve. The modern symphony orchestra usually includes four horns. Though difficult to play and prone to producing conspicuous errors, its tone is widely admired.

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See Horn (instrument)