Significant mental health problems can and do occur in young children. In some cases, these problems can have serious consequences for early learning, social competence, and lifelong health. Furthermore, the foundations of many mental health problems that endure through adulthood are established early in life through the interaction of genetic predispositions and sustained, stress-inducing experiences. This knowledge should motivate practitioners and policymakers alike to address mental health problems at their origins, rather than only when they become more serious later in life. This report summarizes in clear language the most recent scientific advances regarding the importance of addressing emerging emotional and behavioral problems in the early years, and the implications of those findings for policy. [This report was sponsored by The Pierre and Pamela Omidyar Fund.]