Within the past five years, significant strides have been made in the characterization of preschool (3-6 years of age) depression. Advances in this line of research have been made possible by increasing attention to the impact of developmental stage on symptom manifestation and the development of measures that appropriately assess for the presence of these developmentally specific symptoms. Available empirical evidence demonstrates that preschool depression is characterized by a specific and stable symptom constellation, associated impairment, biologic markers, and family history of similar disorders. This article reviews the relatively new body of evidence supporting the validity of preschool depression.