The term trauma is widely used as a general designation for profound psychological injuries, and it seems that everyone knows what it means. However, in the professional field, terms and concepts are still being discussed, particularly in trauma research. Ellert Nijenhuis dedicates his three-part work, of which volumes I and II are presented here together, to the conceptual discussion of trauma research and neurobiological foundations. Volume I aims to overcome the conceptual shortcomings that have affected the field of trauma research to this day. It offers new definitions of the concept of trauma and derived concepts, as well as a new dimension of trauma-related disorders. Nijenhuis demonstrates that individuals and their environment are mutually dependent, influencing and corresponding to each other. Volume I unites two groups of trauma-related disorders.