This study used semi-parametric group-based modeling to explore unconditional and conditional trajectories of self-reported depressed mood from ages 12 to 25 years. Drawing on data from the National Longitudinal Study of Adolescent Health (N = 11,559), 4 distinct trajectories were identified: no depressed mood, stable low depressed mood, early high declining depressed mood, and late escalating depressed mood. Baseline risk factors associated with greater likelihood of membership in depressed mood trajectory groups compared with the no depressed mood group included being female, Black or African American, Hispanic or Latino American, or Pacific Islander or Asian American; having lower socioeconomic status; using alcohol, tobacco, or other drugs on a weekly basis; and engaging in delinquent behavior. Baseline protective factors associated with greater likelihood of membership in the no depressed mood group compared with the depressed mood trajectory groups included 2-parent family structure; feeling connected to parents, peers, or school; and self-esteem. With the exception of delinquent behavior, risk and protective factors also distinguished the likelihood of membership among several of the 3 depressed mood groups. The results add to basic etiologic research regarding developmental pathways of depressed mood in adolescence and young adulthood. (Contains 1 figure, 1 footnote, and 4 tables.)