This article describes the key features of environmental and occupational epidemiology studies, including the types of study designs (incidence studies, incidence case–control studies, prevalence studies, and prevalence case–control studies), methods of measurement of exposure (subjective measures, exposure monitoring, area sampling, and personal sampling), issues of bias (confounding, selection bias, and information bias), and interpretation of environmental and occupational epidemiology studies (consideration of temporality, plausibility, consistency, strength of association, dose–response, and reversibility, as well as the likelihood that findings are due to chance).