Most adolescents progress to adulthood with relatively little difficulty, experiencing excellent physical health and strength and not engaging in behaviors that put themselves or others at risk. Others, however, take many sorts of unhealthy risks—in their sexual behavior, in driving, in substance use, in criminal activity—or experience emotional distress or mental health disorders. For a substantial number of adolescents, the consequences are severe: they may limit a young person’s opportunities to grow into a productive adult, they are the source of lifelong health problems, and they result in a significant risk of injury and death for adolescents.3