The euphonium is a medium-sized, 3 or 4-valve, often compensating, conical-bore, tenor-voiced brass instrument that derives its name from the Ancient Greek word εὔφωνος euphōnos, meaning "well-sounding" or "sweet-voiced" (εὖ eu means "well" or "good" and φωνή phōnē means "sound", hence "of good sound"). As a baritone-voiced brass instrument, the euphonium traces its ancestry to the ophicleide and ultimately back to the serpent. With the invention of the piston valve system c. 1818, the construction of brass instruments with an even sound and facility of playing in all registers became possible.
The euphonium repertoire consists of solo literature and orchestral, or, more commonly, concert band parts written for the euphonium. Since its invention in 1843, the euphonium has always had an important role in ensembles, but solo literature was slow to appear, consisting of only a handful of lighter solos until the 1960s. Since then, however, the breadth and depth of the solo euphonium repertoire has increased dramatically. Finally, the euphonium has, thanks to a handful of enterprising individuals, begun to make inroads in jazz, pop and other non-concert performance settings.