Substance abuse among American youth is a major public health concern and is one of the leading causes of morbidity and mortality during adolescence and across the life course. The Monitoring the Future study is a longitudinal analysis of trends in substance use among American adolescents in grades 8, 10, and 12. In 2003, the sample sizes were 17,000 8th graders, 16,300 10th graders, and 15,200 12th graders. An overview of the key findings indicates that there were broad declines in drug use among American youth during 2003. Most significant was the decline in ecstasy use reported by students in all three grade levels. Marijuana continued its downward trend in prevalence of usage, which was observable in 2002 and 2003 for all three grades. Moreover, perceived risk regarding marijuana use was up for all three grades in 2003. In the general category of illicit drugs other than marijuana, decreases in usage were reported among 10th and 12th graders, while 8th graders usage in this category had leveled out. Tranquilizer use had also declined among students in the upper two grades, despite the steady increase in tranquilizer usage displayed in recent years by 12th graders. Hallucinogens other than LSD demonstrated no decline in use in either 2002 or 2003. Cocaine and crack use held steady overall, but demonstrated usage levels far below those of the mid-1980’s. Club drugs had a low prevalence of use among secondary students. Substances showing signs of increased use included inhalants, OxyContin, and Vicodin. The use of licit drugs, such as cigarettes and alcohol, among American youth is pervasive, with 54 percent of youth reporting cigarette and 77 percent of students reporting alcohol consumption by the end of high school. Concerns emerging from the 2003 survey include the continued leveling off of the decline in drug use among 8th graders. In terms of prevention, the wide divergence in trajectories of drug use indicates that prevention must occur drug by drug. Following the overview, results are presented by drug and subgroup differences are considered for gender, college plans, region of the country, population density, socioeconomic level, and race/ethnicity. Tables