This paper reviews the epidemiology of substance use among adolescents. There is a public health imperative in all countries to assess the population rates of tobacco, alcohol and illicit drug use among adolescents. In addition, monitoring trends over time may reflect the net effects of activities and programs carried out to prevent adolescent substance use. School based surveys provide prevalence estimates of substance use, but do not capture street and homeless youth and other high risk adolescents not found in the school environment. Overall, the results of this review suggest that tobacco, hazardous alcohol use, and most categories of illicit drug use have shown consistent increases in prevalence since about 1990 in most developed countries, for school-based adolescents, suggesting that the substance use problem among adolescents remains unsolved. These trends are remarkably similar across substance use behaviours, and among most developed countries, although limited data has emanated from adolescents in the developing world. Interventions to reduce or prevent substance use have shown mixed results, with those focusing on the adolescents' social environment showing the most promise. Broader public health approaches, including the linkage to community-wide prevention, and greater enforcement or regulatory and legislative approaches to tobacco and alcohol access are future directions for research and practice.