Less than eight years after the establishment of the National Child Traumatic Stress Network in 2001 it has become evident that the current diagnostic classification system is inadequate for tens of thousands of traumatized children. While the inclusion of PTSD in the psychiatric classification system in 1980 led to extensive scientific studies of that diagnosis, over the past 25 years there has been a parallel emergence of the field of Developmental Psychopathology, which has documented the effects of interpersonal trauma and disruption of caregiving systems on the development of affect regulation, attention, cognition, perception, and interpersonal relationships. Another significant development has been the increasing documentation of the effects of adverse early life experiences on brain development. The goal of introducing the diagnosis of Developmental Trauma Disorder is to capture the reality of the clinical presentations of children and adolescents exposed to chronic interpersonal trauma. Whether or not they exhibit some symptoms of PTSD, children who have developed in the context of ongoing danger, maltreatment, and inadequate caregiving systems are ill-served by the current diagnostic system, as it frequently leads to multiple unrelated diagnoses, an emphasis on behavioral control without recognition of interpersonal trauma and lack of safety in the etiology of symptoms, and a lack of attention to ameliorating the developmental disruptions that underlie the symptoms.