This paper presents the available prevalence studies of illicit substance use among migrants and ethnic minorities and discusses their limitations, as well as looking at prevalence and risk factors for substance use among refugees. Two subsections focus on specific issues among non-refugee third-country nationals and Roma. Section 2 of this paper summarises risk and protective factor mechanisms in an ecosocial framework, while sections 3 and 4 are the core of this paper, and focus on social responses targeting migrant and ethnic populations in prevention, treatment and harm reduction, as well as highlighting broader responses which support these interventions. Finally, sections 5 and 6 conclude the report with a discussion of major challenges in addressing drug-related problems among these populations and examine some possible implications for policy and practice.