This book, the third in the series Behavior of Radionuclides in the Environment, is dedicated to Fukushima. Major findings from research since 2011 are reviewed concerning the behavior of radionuclides released into the environment due to the Fukushima Dai-ichi Nuclear Power Plant accident, including atmospheric transport and fallout of radionuclides, their fate, and transport in the soil-water environment, behavior in freshwater, coastal and marine environment, transfer in the terrestrial and agricultural environment. Volume III discusses not only radionuclides dynamics in the environment in the short- and mid-term, but also modeling and prediction of long-term time changes. Along with reviews, the book contains original data and results not published previously. It was spearheaded by the authors from the Institute of Environmental Radioactivity at Fukushima University, established two years after the Fukushima accident, with their collaborators from Japan, Russia, and Ukraine. The knowledge emerging from the studies of the environmental behavior of Fukushima-derived radionuclides enables us to move forward in understanding mechanisms of environmental contamination and leads to better modeling and prediction of long-term pollution effects in general.