[en] The International Union of Radioecologists (I.U.R.) has maintained a vigorous program of activities in accordance with the goals of its charter. To meet these goals, the I.U.R. has sponsored a number of workshops, meetings, and other related activities aimed at improving our ability to understand and predict the consequences of release of radionuclides to the environment. These include: intercomparison and harmonization of methodologies and a continuous feedback between scientists engaged in mathematical modeling and those carrying out field studies. Specialized workshops dealing with problems in understanding transfer coefficients in the terrestrial environment are being held. In the marine environment, long-distance transport in sediments plays an important role for the spread of radioisotopes released from reprocessing plants (e.g., in the Eastern Atlantic, the Northland Baltic Sea). Representatives of the countries concerned (including from Northern Countries) will define conditions of information exchange, sampling (time, character of sediments), and modelisation