A high-capacity magazine ban is a law which bans or otherwise restricts detachable firearm magazines that can hold more than a certain number of rounds of ammunition. For example, in the United States, the now-expired Federal Assault Weapons Ban of 1994 included limits regarding magazines that could hold more than ten rounds. As of 2022, twelve U.S. states, and a number of local governments, ban or regulate magazines that they have legally defined as high-capacity. The majority of states do not ban or regulate any magazines on the basis of capacity. States that do have large capacity magazine bans or restrictions typically do not apply to firearms with fixed magazines whose capacity would otherwise exceed the large capacity threshold.

A magazine, often simply called a mag, is an ammunition storage and feeding device for a repeating firearm, either integral within the gun or externally attached. 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 or cylinder.