An aerophone (/ˈɛəroʊfoʊn/) is any musical instrument that produces sound primarily by causing a body of air to vibrate, without the use of strings or membranes, and without the vibration of the instrument itself adding considerably to the sound. Aerophones categorically comprise "the largest and most complex group of instruments in the Americas".
Aerophones are one of the four main classes of instruments in the original Hornbostel–Sachs system of musical instrument classification, which further classifies aerophones by whether or not the vibrating air is contained within the instrument. The first class (41) includes instruments which, when played, do not contain the vibrating air. The bullroarer is one example. These are called free aerophones. This class includes (412.13) free reed instruments, such as the harmonica, but also many instruments unlikely to be called wind instruments at all by most people, such as sirens and whips. The second class (42) includes instruments which contain the vibrating air when being played. This class includes almost all instruments generally called wind instruments — including the didgeridoo, (423) brass instruments (e.g., trumpet,french horn, baritone horn, tuba), and (421 & 422) woodwind instruments (e.g., oboe,flute,saxophone, clarinet).