Generally, the gun market is too informal and too broadly distributed in time and space to allow for effective police penetration. The opportunity for reduction that does exist may lie at the intersection of the markets for guns and drugs. This observation does not speak to the other major element of control, namely, improving the regulation of licit markets so as to reduce the flow of guns into the illicit market from which a large share of the youth obtain guns. Comparison of the enforcement against drug and gun markets presents at least two analytic challenges. The first is primarily conceptual: identifying what dimensions of an illegal market influence the effectiveness of enforcement. The second is primarily empirical: determining how drug and gun markets compare on these dimensions. Part II of this article identifies the characteristics of illegal markets that impede effective policing, that is, that make it difficult to raise the price or accessibility of the goods or services to the final purchaser. Part III then considers what we know about these characteristics of the illegal markets in which urban youth obtain firearms, particularly handguns. Part IV presents some conclusions about potential strategies for controlling these gun markets. The article considers only the markets for wholly illicit drugs, primarily cocaine, heroin, and marijuana. 1 table and 118 footnotes