Abstract: Posttraumatic stress disorder (PTSD) is a chronic, debilitating, psychological condition that occurs in a subset of individuals who experience or witness life-threatening traumatic events. PTSD is highly prevalent in those who served in the military. In this paper, we present the underlying theoretical foundations and existing research on virtual reality exposure therapy, a recently emerging treatment for PTSD. Three virtual reality scenarios used to treat PTSD in active duty military and combat veterans and survivors of terrorism are presented: Virtual Vietnam, Virtual Iraq, and Virtual World Trade Center. Preliminary results of ongoing trials are presented.