A significant minority of teens and preteens suffer from anxiety disorders, depression and other mood disorders, behavior problems, and drug and alcohol addiction. Others have low self-esteem, difficulty coping, and feelings of insecurity. Given the harmful consequences of such disorders, policymakers and practitioners should be alert to teens mental and emotional health so that they can develop sound prevention and intervention strategies to address these challenges. In an effort to determine the best ways to prevent or address these problems, Child Trends conducted a review of nearly 300 research studies on teens mental health and emotional well-being. This review suggests that mental health programs that use comprehensive, integrated approaches appear to be most effective in preventing such problems as conduct disorder, attention deficit hyperactivity disorder (ADHD), and alcohol and drug abuse. This brief is divided into two parts. The first addresses mental health in adolescence and the second covers emotional well-being. The What Works tables detail some of the programs and approaches that are most likely to succeed in these areas. Only experimentally evaluated programs are included in the review of what works. Also included in the table are some best bets, promising practices drawing on both experimental and quasi-experimental evaluations, other research, and wisdom from practitioners. (Contains 81 references.) (GCP)