The mellophone is a brass instrument that is typically used in place of the French horn in marching bands or drum and bugle corps.

The mellophone has three valves, operated with the right hand. Mellophone fingering is identical to that of a trumpet, not the French horn as is commonly assumed. Mellophones are typically pitched in the key of F. The overtone series is an octave above that of the horn. Many drum and bugle corps, however, use mellophones pitched in G, although the number has dwindled somewhat since the two major United States drum and bugle corps circuits (first Drum Corps International and then Drum Corps Associates) passed rule changes allowing use of instrumentation in any key (although corps using mellophones pitched in G typically have the whole of their brass section also using G instruments, while those using mellophones pitched in F generally have the remainder of their brass section using B♭; instruments). Mellophones, like most brass instruments, are available in a number of keys. Mellophones are usually in either F or E♭, although historically instruments were built to convert to many keys, including B♭, D and C.