This report reflects the work of four national research teams, based in Phnom Penh, Jakarta, Manila and Bangkok, and two central research staff , based at the ASEAN Secretariat in Jakarta. It analyzes information obtained through reviews of the existing literature, interviews with government officials, and examination of government documents, such as intake forms and annual reports. The report starts by taking the issue of “data on trafficking” back to basic principles. What is “data on trafficking”? Why do we need it? How and where do we get it? Drawing on the literature from trafficking, crime prevention, statistics, and information management, this chapter identifies and discusses several best practice principles that should assist governments wanting to improve their data on trafficking in persons. and the final chapter discusses lessons learned from the country studies, including common challenges facing each of the four countries. These challenges suggest practical solutions and recommendations that are potentially relevant to all ASEAN member countries wanting to improve their data on trafficking.