In the UK, a baritone horn (often shortened to baritone) is a bass saxhorn in Bb and is generally known as a tenor horn in the US. A baritone in the US is a tenor saxhorn in Bb.

A valved brass instrument in the tuba family, it is pitched in B flat, the same as a trombone, and has a range of E to b' flat. This instrument is commonly used in brass bands both in America and Europe.

There is a common misconception that all 3-valve instruments are baritones and all 4-valve instruments are euphoniums. This is due to the old practice of American instrument manufacturers calling their top models euphoniums and student models baritones. The differences between the baritone and the euphonium are the shape of the bore and the physical size of the instrument. Although both are transposing instruments in Bb, and both have a nine-foot-long main bugle, the baritone horn, with its smaller bore is more compact, so it is physically smaller. The baritone horn - a saxhorn - is closer in relation to the trombone and trumpet with their cylindrical bores, while the euphonium is closer in nature to the horn and tuba with their conical bores.