Radiation epidemiology seeks to describe and quantify the risk of health effects, often cancer, in populations exposed to ionizing and non-ionizing radiation. To do so, it is important to estimate organ or tissue doses for large numbers of exposed individuals with a moderate to high degree of certainty. Unlike dosimetry for establishing compliance with regulations, which relies on doses estimated for representative, maximally exposed, or highest-risk persons, dosimetry for analytical epidemiological studies usually requires developing new dosimetric models or tailoring existing ones to reach a higher level of individualization. The majority of radiation epidemiological studies conducted to date have required the reconstruction of dose to individuals or study populations that were exposed many years ago. This presents a major challenge to researchers, because measurements often are not available or do not exist in forms that are directly usable for calculating radiation doses on an individual basis. The goal of this special issue of Radiation Research is to introduce readers to an array of dosimetric methods and applications that have been developed to reconstruct radiation exposures for epidemiological studies. We intend to fill a void in the technical literature by describing these methods in terms understandable to epidemiologists, dosimetrists and statisticians so that these research tools can be used by other members of the research community. This publication follows the 1995 National Academy of Sciences/National Research Council report entitled Radiation Dose Reconstruction for Epidemiologic Uses(1). That book summarized the views and expertise of a group of scientists who participated in a workshop on dose reconstruction for environmental radiation exposures. Since then, the methods for dose reconstruction have continued to advance, and the knowledge gained from epidemiological studies of populations exposed to radiation from many different sources has grown. It is therefore timely to publish a special issue of Radiation Research devoted to the methods used to estimate medical, occupational and environ