The visibility and the political import of the collapse of the World Trade Center Towers made it an extraordinary event even in a world replete with disasters and wars. These massive buildings symbolized the financial center of the world. Their dramatic collapse was witnessed directly by millions of people in New York City, and indirectly on television by countless others around the globe. Thousands died, tens of thousands narrowly escaped death, and the effects rippled across communities of a wide region.

The chapters in this part of the book are concerned with the way in which this event affected the mental health of people in New York City and elsewhere in the USA. The authors of three key studies of the mental health effects describe the way in which their research was conceived and executed, and some of their most striking results. Leading psychiatric epidemiologists were invited to critique these studies, and comment more generally on the nature of research on mental health effects of disasters. In addition, one of the study authors was invited to respond to the critiques. We are indebted to all of the authors for their contributions.

By design, therefore, the chapters present divergent viewpoints about the nature and the magnitude of the mental health effects of September 11th. This approach results in a lively exchange, and enables readers to appreciate the ongoing debate and form their own opinions about it. But readers also have a right to know what the editors perceive to be the main lessons of this work. We will highlight five which have clear implications for future studies of the mental health effects of large scale terrorist attacks and other disasters.