The REES group, within the Program in Epidemiology in the Division of Public Health Sciences, conducts multidisciplinary studies of significant public health importance. These epidemiologic studies focus on the identification of risk factors and causes of cancer and other diseases associated with many different types of environmental exposures, including ionizing radiation, persistent organic pollutants, electromagnetic fields and factors that disrupt normal circadian rhythm. REES investigators have conducted many large and complex epidemiologic studies involving collaborators from many scientific disciplines. Their work has focused on breast cancer, thyroid cancer and other thyroid diseases, lymphomas, and myelodysplastic syndrome. The group has maintained a long-standing research program in the Russian Federation to identify cancer risk associated with exposure to radiation from the Chernobyl accident. Some REES investigators (Davis and Kopecky) have also maintained long-standing collaborations with the Radiation Effects Research Foundation in Hiroshima, Japan. Volunteer study participants from around the world have generously contributed their time and effort to provide the detailed information collected by the REES studies.