Firearms, notably handguns and rifles, leave unique markings on the ammunition they fire (both the bullet and the shell casing); these are commonly called "ballistic fingerprints." Two States, Maryland and New York, enacted laws in 2000 that require ballistic fingerprinting of all new handguns sold by licensed firearms dealers in the State. At the time of sale, dealers must provide a shell casing (in Maryland) and/or a bullet (in New York) for inclusion in a database maintained by the State police. At least four other States have considered adopting similar ballistic fingerprinting laws. The purpose of such laws is to aid police investigations of shootings by creating more comprehensive ballistic databases and to act as a deterrent to the criminal use of guns. Regarding the effectiveness of such laws in reducing the supply of guns to criminals and youth, research contradicts the claim that all criminals are so determined and resourceful that they will always do whatever it takes to get a gun, regardless of regulatory obstacles, risk of incarceration, or price of the gun. In addition to providing disincentives for illegal gun sales, ballistic databases can discourage criminals' use of guns. A study conducted in Maryland prior to the enactment of its law indicated that criminally involved youth were acutely aware that police commonly use ballistic evidence to link guns to shootings. Youth who had recently acquired a gun were wary of buying used guns, especially from strangers, because they did not want to be caught with a gun that could be linked to other crimes. In addition to providing support for the rationale behind ballistic-fingerprinting laws, this paper also refutes the various arguments that have been mounted against the effectiveness of such laws. Regarding the wisdom and feasibility of a Federal comprehensive ballistic fingerprinting law, the author argues that such a law would be appropriate if research indicates that existing State laws are helping to solve and deter a significant number of gun crimes; also, the very large size of the database would not substantially reduce its ability to assist in linking guns to crime scenes. A Federal law may be more effective than State laws due to its potential for deterring interstate gun trafficking. The projected high costs of such a system must be weighed against the potential to reduce the enormous social and economic costs associated with gun violence. 17 references and 3 additional resources