A wind instrument is a musical instrument that contains some type of resonator (usually a tube) in which a column of air is set into vibration by the player blowing into (or over) a mouthpiece set at or near the end of the resonator. The pitch of the vibration is determined by the length of the tube and by manual modifications of the effective length of the vibrating column of air. In the case of some wind instruments, sound is produced by blowing through a reed; others require buzzing into a metal mouthpiece, while yet others require the player to blow into a hole at an edge, which splits the air column and creates the sound.

Almost all wind instruments use the last method, often in combination with one of the others, to extend their register.

Wind instruments are typically grouped into two families:

Woodwind instruments were originally made of wood, just as brass instruments were made of brass, but instruments are categorized based on how the sound is produced, not by the material used to construct them. For example, saxophones are typically made of brass, but are woodwind instruments because they produce sound with a vibrating reed. On the other hand, the didgeridoo, the wooden cornett (not to be confused with the cornet), and the serpent are all made of wood (or sometimes plastic), and the olifant is made from ivory, but all of them belong to the family of brass instruments because the vibration is initiated by the player's lips.

In the Hornbostel-Sachs scheme of musical instrument classification, wind instruments are classed as aerophones.

Sound production in all wind instruments depends on the entry of air into a flow-control valve attached to a resonant chamber (resonator). The resonator is typically a long cylindrical or conical tube, open at the far end. A pulse of high pressure from the valve will travel down the tube at the speed of sound. It will be reflected from the open end as a return pulse of low pressure. Under suitable conditions, the valve will reflect the pulse back, with increased energy, until a standing wave forms in the tube.

Reed instruments such as the clarinet or oboe have a flexible reed or reeds at the mouthpiece, forming a pressure-controlled valve. An increase in pressure inside the chamber will decrease the pressure differential across the reed; the reed will open more, increasing the flow of air. The increased flow of air will increase the internal pressure further, so a pulse of high pressure arriving at the mouthpiece will reflect as a higher-pressure pulse back down the tube. Standing waves inside the tube will be odd multiples of a quarter-wavelength, with a pressure anti-node at the mouthpiece, and a pressure node at the open end. The reed vibrates at a rate determined by the resonator.

For Lip Reed (brass) instruments, the players control the tension in their lips so that they vibrate under the influence of the air flowing through them. They adjust the vibration so that the lips are most closed, and the air flow is lowest, when a low-pressure pulse arrives at the mouthpiece, to reflect a low-pressure pulse back down the tube. Standing waves inside the tube will be odd multiples of a quarter-wavelength, with a pressure anti-node at the mouthpiece, and a pressure node at the open end.