In the field of child psychopathology research, a growing number of longitudinal studies have investigated early developmental precursors of maladaptive outcomes (see for reviews: Campbell, 1995; Koot, 1995; Sameroff and Seifer, 1990). The multitude of theoretical assumptions and related risk factors and outcomes represented by these studies calls for a more integrated approach to the study of the development of psychopathology. In such an approach, the developmental psychopathology paradigm and the distinction between internalizing and externalizing psychopathology are especially useful. The developmental psychopathology paradigm is a promising theoretical framework which provides a structured approach to the development of maladaptation across the life-span. This approach centers around the identification of endogenous and environmental factors that are involved in the early origins, course, and detection of psychopathology (Cicchetti and Cohen, 1995a; Koot, 2000). Because of the emphasis on the developmental aspect of psychopathology in this approach, the distinction between internalizing and externalizing expressions of dysfunction is of special interest, since it is the only consistently empirically identified classification across ages (Cicchetti and Toth, 1991). Internalizing disorders are characterized by disordered mood or behavior such as withdrawal, anxiety, or depression, while externalizing disorders are characterized by disordered behavior such as aggression, or delinquency, and hyperactivity (Achenbach and McConaughy, 1997; Cicchetti and Toth, 1991). In the following section, the developmental psychopathology perspective on the early origins, course, and detection of psychopathology will be introduced. This framework and salient gaps in related empirical efforts regarding intemalizing and externalizing psychopathology provide the basis for this thesis.