In firearms, the chamber is that portion of the barrel or firing cylinder in which the cartridge is inserted prior to being fired. Rifles and pistols generally have a single chamber in their barrels, while revolvers have multiple chambers in their cylinder and no chamber in their barrel.

The act of chambering a cartridge means the insertion of a round into the chamber, either manually or through the action of the weapon (e.g. pump-action, lever-action, bolt-action, or automatic action.).