The article reviews the empirical evidence for trafficking and human smuggling in Europe. It argues that a market for irregular migration services has emerged, in which the mechanisms and forms of organization are still relatively unknown. Irregular migrants using these services are exposed both to unscrupulous service providers and to the immigration and policing authorities, thereby generating a dependence on safeguards provided by the trafficking networks. Thus a symbiosis has developed between trafficker and trafficked. The enormous interest and concern for trafficking and human smuggling in governmental, inter-governmental and non-governmental organizations, in the media and popular opinion, is running ahead of theoretical understanding and factual evidence. This has implications for policy measures designed to combat trafficking and human smuggling, which may not work and also have unintended side effects. The article begins with a discussion of the main conceptual and definitional issues confronting researchers and politicians. This is followed by an assessment of the main theoretical approaches that have been developed and an evaluation of current statistical knowledge. Information on the organizational structure of trafficking organizations is then reviewed, followed by a summary of the characteristics of migrants involved, based on empirical studies that have been carried out. The article concludes by indicating some of the main research priorities.