Recent biological models of posttraumatic stress have pointed to the importance of acute reactions in the genesis and maintenance of PTSD. This presentation will review prevailing biological models of trauma response, with specific focus on fear conditioning models. There will be a review of empirical studies of biological markers of adaptive and maladaptive responses to trauma. These studies will include studies of heart rate, neuroimaging, and startle response. The review will then extend biological models to discuss factors that may predispose people to PTSD development and will review the relevant evidence. The review will address evidence concerning the role that neuroimaging evidence has in understanding the treatment of PTSD. Possibilities of enhancing current psychotherapy approaches to PTSD by modulating neurotransmitters associated with learning will be discussed and findings from a range of anxiety disorders will be discussed. Finally, challenges to early intervention will be discussed and the opportunities offered by biological advances will be outlined.