A magazine is an ammunition storage device within or attached to a firearm. The magazine may be integral to the firearm (fixed) or removable (detachable).

The cartridges in the magazine are loaded into the firearm, either automatically or manually depending on the type of gun. Magazines are almost always driven by a spring. Some magazines can in turn be loaded by a clip; calling a magazine a clip is incorrect.

The most common type of magazine is the detachable "box" type (pictured at right.) However, other types are available, such as the "drum" magazine sometimes used with the Thompson submachine gun, the "pan" magazine of the Russian DP-28 machine gun, and the fixed "tube" magazine found on lever-action rifles.

Magazines for a particular firearm may come in different shapes and sizes. Certain magazines are unmistakable in their appearance, such as those of the AK-type assault rifles, while with others it can be more difficult to tell what gun they belong to, such as when comparing the Ruger Mini-14's magazines with AR-15/M16 magazines.