This article, the first of a two-part series, introduces the topic human trafficking in the United States. Based on the literature review, the author delineates definitions of "human trafficking," the extent and types of human trafficking in the United States, characteristics of trafficked victims and perpetrators, the human trafficking data reporting system, and examples of cases in the United States and its territories. The goal is to provide an introduction to this topic for library staff to use in their research and instruction services. Part II, to follow, is a survey of United States government web resources on human trafficking in the United States for publications and data.