The highest incidence for clinical depressions is during adolescence. Furthermore, mental health illnesses that recur over the life-course begin in young people. 70% of all mental health emerge before thirty years of age. Almost all interventions for young people have been first developed for and targeted at adults. Here for the first time is a talking therapy (BPI), that has been developed for, and with, adolescents. After thirty years of clinical experience with mentally ill adolescents and two major randomised controlled trials of treatment, the authors reveal a brief psychosocial intervention that is as effective as CBT for adolescents with depression with and without comorbid anxiety and conduct disorder. BPI can be taught to mental health practitioners in sixteen hours and they can immediately start delivery of care. After a six-month supervision, new BPI practitioners offer an evidence based and NICE approved treatment in their usual clinical practice.