The rapid growth of clinical and research interest in mood disorders in juveniles over the last 20 years was preceded by a long period in which these conditions were discussed only cursorily, or not at all, in textbooks of psychiatry, child psychiatry or paediatrics. This chapter provides evidence about the wider historical background and sets some current clinical and research issues in perspective. It discusses the growth of interest in juvenile mental disorder, changing theories of child mental development, and changing conceptions of childhood. With the subsequent return to near-Kraepelinian concern for descriptive diagnosis and the search for organic causes, fostered by new knowledge and pharmacological treatments, clinical and scientific interest in mood disorders and their pathophysiology began to surface. The historical study of mood disorders in children and adolescents draws attention to many of the issues and questions that continue to call for clinical and research attention.