This chapter explores sex trafficking in the EU with a critical eye to undertaking comparative, cross-national research. To this end, the chapter begins by addressing the definition, nature and scale of sex trafficking as it exists in the EU, and highlights some measurement problems associated with ‘counting’ sex trafficking incidents, which is one of the most illusive organised crime activities. Secondly, the chapter frames the EU’s institutional responses to trafficking victims in the context of broader concerns in connection with unwanted immigration and criminality. In contrast, these concerns are set against the increasing profile that has been given over to victims of crime, at the level of the UN and the European Commission, since the mid-1980s. Finally, the chapter outlines research undertaken by the author in selected EU Member States on criminal justice responses to victims of crime, and, specifically, trafficking victims. Findings from the research are compared using a broad-based checklist of possible victim protection and assistance measures. The promise and problems of trying to compare different legal systems with very different victim-centred practices, and different experiences of sex trafficking, are highlighted with regard to the idea of transferable ‘good practice’ between jurisdictions.