Among the gun control proposals being most actively pushed at the State level is a mandatory penalty, usually a jail sentence of 6 to 12 months, for the unlicensed carrying or possession of handguns or all firearms. Such laws purportedly would deter the carrying of firearms to commit crimes; however, there is no evidence that this has occurred in jurisdictions where such laws are in effect. Criminals who would risk the consequences of committing a violent crime are not likely to be deterred by a mandatory penalty for the unlicensed carrying of a concealed weapon also increases the likelihood that such a case will be dismissed, even when it is associated with a felony charge. Such laws have the effect of either deterring citizens from carrying guns to protect themselves in high crime areas, thus making them more vulnerable to victimization, or of incarcerating noncriminals for an essentially victimless crime. Moreover, mandatory sentencing tends to increase the use of police discretion and the possibility of the unequal application of the law. Strict enforcement can also have the effect of increasing court caseloads and jail populations involving persons without prior criminal records -- a questionable use of criminal resources. This critical assessment of mandatory sentencing for the unlicensed carrying or possession of firearms is borne out in a careful analysis of the impact of Massachusetts' Bartley-Fox law. Fifteen notes and 26 references are provided.