A brass instrument is a musical instrument that uses a cupped mouthpiece shaped in a way that allows the player's lips to vibrate to generate the instrument's sound. Brass instruments are usually, but not invariably, made of brass. Similarly, in musical terms, not all instruments constructed from brass belong in the category of "brass instruments"; a notable example is the saxophone, which, although usually made of brass, is a woodwind instrument.
Because the player has direct control of the prime vibrator (the lips), brass instruments exploit the player's ability to select the harmonic at which the instrument's column of air will vibrate. By making the instrument about twice as long as the equivalent woodwind instrument and starting with the second harmonic, players can get a good range of notes simply by varying the tension of their lips (see embouchure). Brass players call each harmonic a "partial".
Brass instruments generally come in one of three families:
- Natural brass instruments, where the player can only play notes in the instrument's harmonic series, for example the bugle. The trumpet was a natural brass instrument prior to about 1795, and the French horn before about 1820.
- Valved brass instruments use a set of valves (typically 3 or 4 but as many as 7 or more in some cases) operated by the player's fingers that introduce a additional lengths of tubing into the instrument, changing its overall length. This family includes the modern trumpet, cornet, flugelhorn, saxhorn, euphonium, tuba, Sousaphone, mellophone, and French horn. The valves are usually piston valves, but can be rotary values. Rotary valves are the norm for the French horn and are also prevalent on the tuba.
- Slide brass instruments use a slide to change the length of tubing. The main instrument in this famility is the trombone (although some valve trombones are also made) and the slide trombone's ancestor the sackbut. Some modern trombones also have rotary valves in addition to the slide. The folk instrument the bazooka is also in the slide family.
- Keyed or Fingered brass instruments used holes along the body of the instrument, which were covered by fingers or by finger-operated pads (keys) in a similar way to a woodwind instrument. These included the cornett, serpent and keyed trumpet. Such instruments were difficult to play and became obsolete with the invention of the valve.
For a comparative list of the pitch of various brass instruments see pitch of brass instruments.