Developmental psychopathology (DP), broadly defined as the scientific discipline that has as its primary goal the integration of developmental science and psychopathology into a coherent approach to explanatory models for psychopathological development, has become the dominant approach in the past decade for understanding the origins of mental disorders among children and adolescents. Hence, it is incumbent upon those working in the field of clinical pediatrics to have at least a basic understanding of its core principles of DP. This article provided such an understanding (i.e., a primer) in an exposition of the four principles that are generally considered be core elements of with examples illustrative of each of the principles.