This study will establish whether sleep EEG dysregulation (low inter- and intrahemispheric coherence) is a reliable feature of childhood and adolescent depression, contrasting symptomatic and remitted children and adolescents with age- and gender-matched normal controls. The long range objective of identifying reliable biological features of depression is to improve on differential diagnosis, prognostication, and treatment selection. Of particular relevance to this application is the additional potential to identify patients prior to the clinical expression of the illness in order to ultimately intervene to prevent the onset of illness. The specific aims are: 1) To establish which sleep EEG coherence measures are significantly lower in those with childhood depression (n=50) compared to age- and gender-matched health controls (n=50). 2) To establish which sleep EEG coherence measures are significantly lower in those with adolescent depression (n=50) compared to age- and gender-matched healthy controls (n=50). 3) To fully explore gender differences in sleep EEG coherence measures in the total sample of depressed (n=100) and control (n=100) and control (n=100) subjects. Equal numbers of males and females will be included in the total sample. We expect that gender differences will be evidence in adolescents with MDD. 4) To explore state-train characteristics of low-inter and intrahemispheric coherence in depressed children and adolescents. 5) A sub-aim is to evaluate the developmental time course of sleep EEG coherence in the 100 healthy controls as a means of determining how high inter- and intrahemispheric coherence measures are influenced by brain maturation. 6) To establish the relationship between sleep micro- and macro- architecture in childhood and adolescent MDD.