A brass instrument of the tuba family, smaller and higher in pitch than a tuba, with a range of B-flat below the bass clef to B-flat in the treble clef.

The concertmaster Sommer of Weimar designed the euphonium in 1843, which was a wide-bored valved bugle in the baritone range and was then called the Euphonion.

The euphonium is mostly used in concert bands and military bands and has taken the place of Richard Wagner's tenor tuba. All of the music originally written for the tenor tuba is now typically performed on the euphonium.

The euphonium is constructed in the way that it looks like a miniature tuba. It contains a conical bore and a flared bell, with four valves.