In order to determine how human trafficking cases are identified and reported by the police, the research team examined just over 600 human trafficking investigations and interviewed law enforcement and crime-reporting personnel in each study site. Interviews were also conducted with victim service providers and non-law enforcement agencies in each community regarding how they identify and report human trafficking victimizations. The research team determined how often human trafficking victims are identified across multiple administrative data systems in each community. Using Multiple System Estimation (MSE) procedures that compare information about identified human trafficking victims in the data systems of multiple providers in the three communities, the research team identified how often human trafficking victims are identified across multiple administrative data systems. MSE procedures were used to estimate the number of sex and labor trafficking victims in each study community. This gauged the degree to which law enforcement data on human trafficking offenses represent the population of human trafficking victims in a community. One of the 10 major findings summarized from this study is that given the issues associated with the identification and reporting of human trafficking, it is likely that the Uniform Crime Reporting (UCR) program undercounts both the human trafficking victims who are identified by local law enforcement due to offense reporting problems and undercounts human trafficking victims in local communities. 7 tables, 3 figures, and 31 references