This chapter describes the terrorist attacks of September 11, 2001, in New York City. It discusses the accumulated efforts of some of the many clinicians, researchers, and mental health professionals who responded in the weeks and months following the attacks. Evidence from the bombing of the Murrah Federal Building in Oklahoma City indicated that over a third of those directly exposed had symptoms consistent with posttraumatic stress disorder (PTSD) 6 months after the event. This finding led to fears of a potential massive mental health crisis in the immediate aftermath of the September 11 terrorist attacks. The overall prevalence of posttraumatic stress disorder (PTSD) in NYC in the immediate aftermath of the attack was approximately 6%, dropping to 1% 6 months later. In the aftermath of September 11, New York City's already taxed social and mental health services were called upon to service an entire city in crisis.