Research on depressive phenomena during adolescence has focused on 3 separate constructs: depressed mood, depressive syndromes, and depressive disorders. Approaches to the assessment, taxonomy, and diagnosis of these 3 conceptualizations are reviewed. Each of the approaches is represented by different assessment tools measuring related but distinct aspects of depressive phenomena. The constructs share a common set of symptoms reflecting negative affectivity but differ in their inclusion of symptoms of anxiety, somatic problems, and disrupted concentration and in the duration and severity of the symptoms they include. Depressed mood, syndromes, and disorders are integrated as 3 levels of depressive phenomena in a hierarchical and sequential model, and moderating factors are hypothesized to account for the relationships among the 3 levels. The need for a stronger developmental focus to understand depressive phenomena during adolescence is emphasized.