The field of behavioral health has increased recognized the importance of addressing the needs of specific age groups with respect to both mental and substance use disorders. Teenagers (aged 12-17) and young adults (aged 18-24) are two age groups for which sensitivity to age is especially importnat in the practice of prevention, treatment, and recovery. What are the most effective approaches to preventing underage drinking and the use of illicit drugs - including the nonmedical use of prescription medications - among youth?