Posttraumatic stress disorder (PTSD) describes a syndrome in which a trauma survivor experiences an inability to get the event out of his/her mind. The symptoms of PTSD were initially conceptualized as resulting from the cascade of biological and psychological responses following the activation of fear and other brain systems. In the last decade, scientific developments have led to a better understanding of why only certain individuals develop this disorder. Furthermore, studies of the neurobiology of PTSD have delineated specific alterations that help shape our understanding of how biological and psychological responses at the time of traumatic events may have long-term consequences. This review will discuss these new findings and their treatment implications.