Environmental epidemiology focuses on identifi cation of environmental exposures that contribute to or protect against injuries, illnesses, developmental conditions, disabilities and deaths, and on identifi cation of public health and health care actions to avoid, prepare for, and effectively manage the risks associated with harmful exposures. Air pollution represents the most common type of such exposure and is defi ned as the introduction of chemicals, particulates, or biological materials that cause discomfort, disease, or death to humans in the atmosphere. Compared with other harmful factors that may affect human development and health, such as exposure to tobacco smoke, exposure to air pollution cannot be fully avoided and affects large numbers of individuals. In addition, although an individual hazard may be smaller than in the case of other harmful factors, the ubiquitous distribution makes it of interest from epidemiology and public health perspective.