Questions about possible links between the onset of cancer and a population’s immediate environment date back to the early 20th century. While their exact role remains a subject of controversy, the role of environmental factors in the development of certain cancers is now widely accepted. These factors, along with genetic and socioeconomic factors, help explain certain disparities in incidence observed internationally. This complex issue of the link between cancer and the environment has become one of the major challenges in contemporary epidemiology.