The authors summarize the regulatory frameworks for the possession of firearms in Mexico, the United States and Canada, and discuss the potential impact of reducing the supply of illicit firearms from the United States into Canada and Mexico. Analysis of publicly available information on the sources of firearms used in criminal enterprise indicates that the United States is a major supplier of illegal handguns to Canada and illegal firearms of all types to Mexico. The vastly different laws governing both the possession of firearms, and commerce in firearms led to cross-border firearms trafficking. Data concerning the misuse of firearms indicates that the United States supplies a large, but unknown share of handguns used in crime in Canada, and that the United States is likely the main source of crime guns in Mexico. The lack of hard data regarding the source of crime guns restricts the ability of researchers to reach conclusions on the effects of increased interdiction of smuggled firearms. Table, figure, and references