Brass instruments are wind instruments, such as the trumpet, French horn or trombone, made of brass or another metal, with a funnel-shaped mouthpiece. Sound is produced through vibration of the lips and adjustment of the length of the sound tube by means of valves or a slide. Brass instruments, unlike any of the other instrument types, rely on the player to produce the vibration that causes the sound. With brass instruments, the player's lips vibrate against a mouthpiece.

Instruments in this category include trumpets, cornets, bugles, flugelhorns, alto horns, French horns, tubas, trombones, baritones, euphoniums, and sousaphones.

Brass instruments distinguish themselves by the way they manipulate the air that travels through them. Most of these types of instruments incorporate "on and off" valves. These valves either extend or shorten the path of the airway. When this happens, the air must travel longer or shorter distances, which causes the frequency of the sound to change.

Large brass instruments are often too cumbersome or heavy for a child younger than age nine. Also, playing these instruments requires significant breath control and special mouthing techniques, so most experts recommend brass instruments for older children. Some students may begin learning the trumpet at an earlier age, but it depends partly on the development of the four front teeth. It is difficult to start if the child still has baby teeth, especially when he or she loses them.