This publication gives a comprehensive assessment of scientific evidence about risk factors linked to diseases and human health hazards, which has important implications for public health policies. Topics discussed include: childhood and maternal undernutrition; nutritional and physiological risk factors; addictive substances; sexual and reproductive health; environmental and occupational risks, including air pollution, unsafe water and sanitation, and climate change; the distribution of risk factors by poverty; data analysis and results; multiple risk factor assessments; and future research.