In the United States, the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) is the primary federal agency overseeing all legitimate businesses that deal with firearms, with the exception of firearms made before January 1, 1899 or muzzle loading firearms. The ATF is in charge of the licensing of all legitimate firearms dealers and gunsmiths in the US that engage in business with the public. The issuance of a Federal Firearms License (FFL) involves a thorough background investigation and an inspection of the gunsmith's premises by an Agent of the ATF. The ATF requires all gunsmiths to record all repairs, noting the serial numbers, type of firearm, caliber or gauge, and full particulars of the owner, with an accepted form of Identification ID to be presented and recorded. Gunsmiths are required to maintain these records in a permanent, non-alterable form. As of 2021, there were over 53,000 ATF-licensed gun shops in the United States.