Book excerpt: Provides a comprehensive assessment of the scientific evidence on prevalence and the resulting health effects of a range of exposures that are know to be hazardous to human health, including childhood and maternal undernutrition, nutritional and physiological risk factors for adult health, addictive substances, sexual and reproductive health risks, and risks in the physical environments of households and communities, as well as among workers. This book is the culmination of over four years of scientific equiry and data collection, know as the comparative risk assessment (CRA) project.