A magazine is an ammunition storage and feeding device for a repeating firearm, either integral within the gun (internal/fixed magazine) or externally attached (detachable magazine). The magazine functions by holding several cartridges within itself and sequentially pushing each one into a position where it may be readily loaded into the barrel chamber by the firearm's moving action. The detachable magazine is sometimes colloquially referred to as a "clip", although this is technically inaccurate since a clip is actually an accessory device used to help load ammunition into a magazine.

Magazines come in many shapes and sizes, from tubular magazines on lever-action and pump-action firearms that may tandemly hold several rounds, to detachable box and drum magazines for automatic rifles and light machine guns that may hold more than one hundred rounds. Various jurisdictions ban what they define as "high-capacity magazines".