As one of the few resources to thoroughly examine the critical problem of over-diagnosis in psychiatry today, this title covers how over-diagnosis in psychiatric practice may lead to over-treatment. It considers the complications of the DSM-5 classification system, with particular reference to major depression, bipolar disorder, Post-traumatic Stress Disorder (PTSD), and Attention-Deficit Hyperactivity Disorder (ADHD). While each of these conditions have given rise to diagnostic fads and epidemics, the classification of mental disorders remains provisional without any biomarkers for mental disorders. It then covers the importance of conservative diagnoses, recognizing that normal variants are not necessarily disorder, and that in many cases, under-, rather than over-diagnosing may be best practice.