This publication features papers presented at the Workshop on Cleaning Up Sites Contaminated with Radioactive Materials, held in Moscow in June 2007. This activity was organized by the National Academies in cooperation with the Russian Academy of Sciences and with funding provided by the Russell Family Foundation. The workshop was designed to promote exchanges of information on specific contaminated sites in Russia and elsewhere and to stimulate greater attention to the severity of the problems and the urgent need to clean up sites of concern to the local and international communities.