This paper summarizes characteristics of major depressive disorder (MDD) in the Oregon Adolescent Depression Project, using data from 816 participants (56% female; 89% White). Contrasting four developmental periods (Childhood [5-12.9], Adolescence [13-17.9], Emerging Adulthood [18-23.9], Adulthood [24-30]), we examine MDD incidence/recurrence, gender, comorbidity, duration, and suicide attempts across periods. MDD first incidence was lower in Childhood compared to subsequent periods, and higher in Emerging Adulthood than Adulthood. Cumulative incidence was 51%. Recurrence was lower during Childhood than remaining periods, which were comparable. Female gender predicted first incident MDD in all four periods but was unassociated with recurrence. Comorbidity rates were comparable across periods. MDD duration was greater in Childhood than remaining periods. Suicide attempt rates were significantly higher during Adolescence than either Emerging Adulthood or Adulthood. Depression research should focus on MDD during Emerging Adulthood, adolescent suicidal behavior, the continuing role of gender into adulthood, and the ubiquity of MDD.