The effects of environmental exposure, broadly defined as any exposure from outside the body, on human health are unquestionably the most important determinants of public health. While important genetic determinants of disease exert their effects irrespective of exposure from outside the body, these do not contribute as much to the overall public health burden of disease as factors such as tobacco smoke, poor quality water, inadequate or contaminated food, occupational exposures to dusts and chemicals, motor vehicle accidents, interpersonal violence, air pollution, and other factors external to the body. In many cases, genetic predisposition and environmental exposures combined cause disease in an individual, so it may be impossible to separate out individual biological contributions from various external factors. Nevertheless, it is widely understood that public health concerns populations and communities, and that environmental determinants of health have been paramount throughout human history.