The systematic study of how available weapons influence the rates, patterns, and outcomes of criminal violence is new, but it is now a well-established and fast-growing subfield in criminology, legal studies, public health, and economics. This review focuses on the transactions that arm dangerous offenders, noting that if those transactions could be effectively curtailed it would have an immediate and profound effect on gun violence and homicide rates. Guns are legal commodities, but violent offenders typically obtain their guns by illegal means. Our knowledge of these transactions comes primarily from trace data on guns recovered by the police and from occasional surveys of gun-involved offenders. Because most guns used in crime are sourced from the stock of guns in private hands (rather than a purchase from a licensed dealer), the local prevalence of gun ownership appears to influence the transaction costs and the proportions of robberies and assaults committed with guns rather than knives or other weapons. Nonetheless, regulations that govern licensed dealers have been linked to trafficking patterns and in some cases to the use of guns in crime.

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