The family of wind instruments which are usually made of a brass or silver tube (either cylindrical or conical bore) that flares into a bell at the end, have cupped mouthpieces similar to that of a trumpet, and usually have valves or slides. A tone is produced by vibration of the lips as the player blows into a tubular resonator (mouthpiece).

To change pitch on a brass instrument, two things come into play: the pressing of valves or the movement of a slide to effectively change the length of the tubing, and the player's lip aperture or 'embouchure' setting, which determines the frequency of the pulsed air or vibrations into the instrument.

It is generally accepted that the term 'brass instrument' should be defined by the way the sound is made, as above, and not by whether the instrument is actually made of brass. Thus, there are brass instruments made of wood, like the alphorn, the cornett and the serpent, while many woodwind instruments are made of brass, like the saxophone.