The work described in this book investigates the development of internalizing (e.g. depression and anxiety) and externalizing (e.g. aggression and hyperactivity) problems from age 2 to 12, and investigates how and why some children exhibit pure or co-occurring internalizing and externalizing psychopathology. This question is especially appealing because even though internalizing and externalizing problems are two disorders from different diagnostic classes and represent separate forms of psychopathology they tend to co-occur in the individual. The findings indicated that psychopathological problems are established early in development and that children may exhibit only internalizing, only externalizing or both types of problems. The risk groups differed in terms of antecedents (cognitive abilities, temperament, home environment) and outcomes (peer relationships, delinquency). The findings of the current work are important for parents trying to understand the development of aggression and depression. Moreover, the book provides important information to psychologists, psychiatrists, and researchers investigating the development of internalizing and externalizing psychopathology.