During the last decade the number of studies about human trafficking increased. This review of research and data on trafficking shows that despite the growing literature on trafficking around the world, relatively few studies are based on comprehensive or empirical research. Besides, information on the actual numbers of people trafficked remains unclear. The book suggests different ways in which to improve research and data on human trafficking. It is an offprint of the special issue of International Migration Vol. 43 (1/2) 2005.