To explore current and innovative sampling methods, technological approaches, and analytical strategies for estimating the prevalence of sex and labor trafficking in vulnerable populations, a 2-day public workshop, Approaches to Estimating the Prevalence of Human Trafficking in the United States, was held in Washington, D.C. in April 2019. The workshop brought together statisticians, survey methodologists, researchers, public health practitioners, and other experts who work closely with human trafficking data or with the survivors of trafficking. Participants addressed the current state of research on human trafficking, advancements in data collection, and gaps in the data. They discussed international practices and global trends in human trafficking prevalence estimation and considered ways in which collaborations across agencies and among the U.S. government and private-sector organizations have advanced counter-trafficking efforts. This proceedings summarizes the presentations and discussions of the workshop.