Concept and recent topics on environmental epidemiology have been introduced in the article. First, the authors presented the basic concept on epidemiology. Answers to the question "Is a particular exposure influent to human health?" can be obtained only from studies of human beings, using an epidemiologic approach. Environmental epidemiology is an application of epidemiology to environmental problem. Then, we presented four examples on environmental epidemiologic research. The four recent topics are residential radon exposure and lung cancer, ingested arsenic and cancer, increase incidence of childhood leukaemia around the English neuclear reprocessing facilities, and magnetic field and excess incidence of childhood leukaemia near Swedish high-voltage power lines.