The euphonium (English: /juˈfoʊniːəm/ yoo-FOH-nee-əm; Italian: eufonio; Spanish: bombardino) is a tenor- and baritone-voiced valved brass instrument pitched in 9-foot (9′) B♭ an octave below the B♭ trumpet or cornet, employed chiefly in brass, military, and concert bands. The euphonium is a member of the large family of valved bugles, along with the tuba and flugelhorn, characterised by a wide conical bore. Most instruments have four valves, usually compensating piston valves, although instruments with four or five rotary valves are common in Eastern and Central Europe.
Euphonium repertoire can be notated in concert pitch in the bass clef, or in the treble clef as a transposing instrument in B♭. In British brass bands, it is typically treated as a treble-clef instrument, while in American band music, parts may be written in either treble clef or bass clef, or both. A musician who plays the euphonium is known as a euphoniumist, a euphonist, or simply a euphonium player.