Abstract
Diagnostic criteria relating to trauma, in ICD-11 and DSM 5, are presented as lists of symptoms with no attempt at understanding the mechanisms of trauma, or at seeing them in the context of human biological and social systems. This seriously limits their usefulness to the psychological therapist. This paper is an attempt at such an understanding, starting from the perspective of the biological fear system. It argues that trauma is an autonomic nervous system dysfunction in which fear responses cannot de-activate, and that complex trauma is
the chronic failure of fear system de-activation and the impact of this failure on a wide range of other systems with detrimental consequences for physical and mental health and social integration.