The study analyzed multiple Chicago Police Department (CPD) administrative datasets, conducted ethnographic interviews with gun brokers and gang leaders, and surveyed inmates in facilities of the Illinois Department of Corrections. The interviews indicated that respondents were extensively involved with guns and violence. Ninety-three percent of respondents said they had been targets of a gun shot on at least one occasion, and just over 40 percent reported having been shot and wounded at least once. About 77 percent of respondents reported possessing a gun within 6 months before their arrest. None of the individuals interviewed was eligible for an Illinois gun license that authorized him to purchase a gun legally, so respondents were able to provide information on the secondary gun market in Chicago. As hypothesized, less than 1 percent of the guns respondents possessed within 6 months of their arrests were purchased from a store. Most were obtained from voluntary transactions with friends and acquaintances in their social network. The transactions included purchases, trades, loans, gifts, and sharing arrangements. Only 7 percent indicated acquiring a gun by theft. Ammunition was also obtained from street sources; however, about 15 percent of respondents reported that someone else straw-purchased ammunition for them. Unexpectedly, there was no indication that self-professed gang members had an easier time than non-gang members in accessing a gun. The lag time between acquiring a gun and using it in a crime tended to be brief, generally 1 month. Because of a general mistrust of police, respondents were reluctant to provide information to police about the underground gun market. Appended list of dissemination reports for this project