One of the most challenging problems facing researchers is the fact that most of the populations relevant to the study of human trafficking, such as victims/survivors of trafficking for sexual exploitation, traffickers, or illegal migrants are part of a “hidden population”, i.e. it is almost impossible to establish a sampling frame and draw a representative sample of the population. The papers dealing with research methods highlight some of the key problems encountered when conducting trafficking research. They have been placed at the beginning of this volume as trafficking research has been criticized in the past for saying little about the methods used to collect and analyse data (see, in particular, the chapter by Kelly). One of the aims of this publication is to suggest ways in which the research methods used to study trafficking could be made more robust. The volume also includes a human trafficking bibliography organized by region and the Notes and Commentary Section includes a meeting summary on “Identifying and serving child victims of trafficking”.