The crime of human trafficking is complex and dynamic, taking place in a wide variety of contexts and frequently difficult to detect. One of the greatest challenges in developing targeted counter-trafficking responses and measuring their impact is the lack of reliable, high-quality data. Historically, available data on human trafficking have been extremely limited and the data that do exist are too often isolated in silos, leading to fragmented knowledge. This Data Bulletin examines some of the main global sources of human trafficking data, their strengths and limitations, and the work IOM and other organizations are carrying out to build the evidence base on human trafficking in the context of the Global Compact for Safe, Orderly and Regular Migration, specifically Objectives 1 and 10.