Approximately 72 percent of youth in the United States report using alcohol at least once and 47 percent report using illicit drugs at least once by the time they reach 12th grade. While the majority of youth who use substances will not develop a substance abuse disorder, substance abuse and addiction are major public health problems affecting approximately 9 percent of the U.S. population age 12 and older. The majority of individuals with substance abuse disorders began using substances during adolescence or even childhood. This course briefly reviews the classes of psychoactive substances, including alcohol, tobacco, and illicit drugs and their basic neurophysiological effects before exploring the historical, social, and psychological factors related to substance use and abuse in adolescents and children. The second half of the course considers substance abuse prevention, treatment, and policy related to children and adolescents.