Major (unipolar) depression is one of the most common mental health disorders in children and adolescents, with an estimated one year prevalence of 4-5% in mid-late adolescence. Depression is probably the single most important risk factor for teenage suicide, the second to third leading cause of death in this age group and a forerunner of adult depressive disorder. Half of those with lifelong recurrent depression started to develop their symptoms before the age of 15 years.