The September 11, 2001, terrorist attack on the World Trade Center in New York City and the environmental aftermath were unprecedented. Airborne dust from the collapse of the towers blanketed Lower Manhattan and was blown or dispersed into many of the surrounding office buildings, schools, and residences. This report from the Office of the Inspector General of the Environmental Protection Agency (EPA) addresses the following six questions: 1. Did the available monitoring data and analyses of that data support EPAs major public communications regarding air quality and associated health risks resulting from the collapse of the World Trade Center (WTC) towers. 2. Were EPA actions and decisions in regard to evaluating, mitigating, and controlling risks to human health from exposure to indoor air pollutants in the WTC area consistent with applicable statutes, regulations, policies, guidance, and practice. 3. Were asbestos demolition and renovation work practice standards followed during WTC cleanup and recovery operations and, if not, why not. 4. To what extent were EPA and government communications regarding air quality and associated health risks: (a) received by the public; (b) understood by the public; and (c) effective in getting people to take the desired actions to reduce their potential health risks. 5. What additional actions, if any, should EPA take to improve its response and recovery efforts in the WTC area related to ambient and indoor air quality. 6. Should EPA revise its preparation and contingency planning for dealing with air pollution resulting from environmental catastrophes.