The study focused narrowly on one of the most understudied aspects of human trafficking in the U.S.: the role of street gangs as facilitators of sex trafficking. Researchers gathered and analyzed data from hundreds of current and former gang members, schools, law enforcement agencies and victim service providers. This three-year project had three primary goals: 1) Determine the role of street gangs in facilitating sex trafficking in San Diego County; 2) Determine the scope of sex trafficking victimization in San Diego County; and 3) Estimate the regional commercial sex economy in San Diego County. Findings centered on: gang involvement, at least 110 gangs are involved in the exploitation of individuals for commercial sex in San Diego and members made up an estimated 85 percent of pimps/sex-trafficking facilitators in the area; victimization, there are 8,830 and 11,773 victims/survivors of sex trafficking every year of whom 1,766 came into contact with law enforcement; regional commercial sex economy, sex trafficking produces an estimated $810 million annually in San Diego, making it San Diego’s second-largest underground economy after drug trafficking; clients, demand is widespread and clients of commercial sex come from all socioeconomic and ethnic backgrounds; and recruitment, the average age of entry into child commercial sexual exploitation was 15 years old and significant recruitment occurred on high school and middle school campuses. The study is a large-scale model of collaborative research and serves as a national model for designing future research on human trafficking in other communities for academic purposes and for use in developing evidence-based policy and practical responses.