Historically, teen depression has been seen as a symptom of other problems such as anxiety, irritability, mood swings, somatic complaints, substance use, and poor school performance. These symptoms were often considered as part of "adolescent turmoil"--a normal, understandable, and even expected phenomenon. For a long time, this viewpoint masked depression problems among youth and made it extremely difficult to diagnose youth depression. More recently, however, Mood Disorders have been reported as one of the most common psychiatric disorders among children and adolescents (Merikangas et al., 2010). Considering the growing concern of teen depression and its possible detrimental impact on various spheres of adolescent functioning, it is imperative for individual youth, their parents, educators, professionals in the human services profession, and youth workers to better understand and recognize the onset, progression, and prognosis of teen depression. This introductory article overviews the ecology of teen depression, including definitions and prevalence, warning signs, antecedents and resilient factors, and the consequences of youth depression. It concludes with a brief summary of the current state of research on youth depression that is applicable to practitioners' work. (Contains 1 table.)