Even though research in the fields of school psychology, child clinical psychology, and child psychiatry has grown exponentially over the past twenty-five to thirty years, no single volume has attempted to comprehensively organize and describe these findings. That is the mission of this forty chapter Handbook, which is organized into the following sections: 1) Assessment; 2) Diagnosis and Classification; 3) Characteristics, Etiologies, and Interventions; 4) Prevention; 5) Ethics, Standards, and Policies; 6) Professional Training and 7) Research Methods