Just as it has for the nation as a whole, the world in which emergency responders work has changed in fundamental ways since September 11, 2001. Members of professions already defined by their high levels of risk now face new, often unknown threats on the job. At a basic level, the September 11 terrorist events have forced emergency responders to see the incidents they are asked to respond to in a new light. At the World Trade Center, 450 emergency responders perished while responding to the terrorist attacks-about one-sixth of the total number of victims. Hundreds more were seriously injured. In this light, the terrorist events are also forcing emergency responders to reconsider the equipment and practices they use to protect themselves in the line of duty. Preparation is key to protecting the health and safety of emergency responders, and valuable lessons can be learned from previous responses. To this end, the National Institute for Occupational Safety and Health (NIOSH) sponsored and asked the RAND Science and Technology Policy Institute to organize a conference of individuals with firsthand knowledge of emergency response to terrorist attacks. The purpose of the conference was to review the adequacy of personal protective equipment (PPE) and practices, such as training, and to make recommendations on how the equipment and practices worked and how they might be improved. Attendees included persons who responded to the 1995 attack on the Alfred P. Murrah Federal Building in Oklahoma City, the September 11 attacks on the World Trade Center and the Pentagon, and the anthrax incidents that occurred during autumn 2001. They represented a wide range of occupations and skills: firefighters, police, emergency medical technicians, construction workers, union officials, and government representatives from local, state, and federal agencies. The conference was held December 9-11, 2001, in New York City, and this report synthesizes the discussions that took place there. Although the terrorist incidents shared some characteristics with large natural disasters, the NIOSH/RAND conference participants highlighted ways in which those incidents posed unique challenges. They were large in scale, long in duration, and complex in terms of the range of hazards presented. As a result of these characteristics, these events thrust responders into new roles for which they may not have been properly prepared or equipped. The themes of scale, duration, and range of hazards were repeated frequently during the discussions at the conference because they were seen as having critical implications for protecting the health and safety of emergency responders-during both the immediate, urgent phase and the sustained campaign phase of the responses.