This document discusses depression, including its symptoms, criteria for diagnosis, prevalence, and treatment approaches. Depression exists on a continuum from normal mood fluctuations to more severe abnormal mood lowering with functional impairment. It is a persistent and pervasive condition with a wide range of psychological and physical symptoms. Treatment involves both antidepressant medication and talking therapies, with the goals of explaining depression, setting a treatment plan and review schedule, and preventing future episodes.