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.

Free aerophones are instruments where the vibrating air is not enclosed by the instrument itself. Free reed instruments such as the accordion, harmonica and reed organ fall into this category.

Non-free aerophones are instruments where the vibrating air is contained within the instrument. Often called wind instruments, they are typically divided into two categories: woodwind and brass. Some, such as the flute, are reedless and produce sound from the flow of air (usually the player's breath) across an opening. Others, such as the clarinet, produce sound by the player's breath being directed against a lamella or pair of lamellae which periodically interrupt the airflow and cause the air to be set in motion. Brass instruments produce sound by sympathetic vibration of air in a tubular resonator in sympathy with the vibration of the player's lips.