It is the unique mission of the Health Hazard Evaluation Program within the National Institute for Occupational Safety and Health (NIOSH) to respond to requests to investigate previously unknown potential occupational health hazards and known health hazards found in new occupational settings. In contrast to other NIOSH programs, the Health Hazard Evaluation Program is not primarily a research program. Rather, it investigates and provides advice to workplaces in response to requests from employers, labor unions, and federal agencies. The National Research Council was charged with evaluating the NIOSH Health Hazard Evaluation Program and determining whether program activities resulted in improvements in workplace practices and decreases in hazardous exposures that cause occupational illnesses. The program received scores of 4 for both relevance and impact, on scales from 1-5, with 5 as the top score. Even though the Health Hazard Evaluation Program is very strong overall, this book makes several recommendations that could help advance the program beyond its current strengths.