The baritone horn, or sometimes just 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.

In the UK, the baritone horn is part of the standardised instrumentation of brass bands. In concert band music, there is often a part marked baritone, but these parts are most commonly intended for, and played on, the euphonium. A baritone can also play music written for a trombone due to similarities in timbre and range.