The baritone horn, sometimes called baritone, is a low-pitched brass instrument in the saxhorn family. It is a piston-valve brass instrument with a bore that is mostly conical, like the higher pitched flugelhorn and alto (tenor) horn, but it has a narrower bore compared to the similarly pitched euphonium. It uses a wide-rimmed cup mouthpiece like that of its peers, the trombone and euphonium. Like the trombone and the euphonium, the baritone horn can be considered either a transposing or non-transposing instrument.

A brass instrument is a musical instrument that produces sound by sympathetic vibration of air in a tubular resonator in sympathy with the vibration of the player's lips. Brass instruments are also called labrosones or labrophones, from Latin and Greek elements meaning 'lip' and 'sound'.