A textbook written by teachers of the Department of Radiochemistry, Faculty of Chemistry, Moscow State University, is devoted to one of the pressing problems of environmental protection. The entry of natural and man-made radionuclides into the environment is considered, special attention is paid to the behavior of radionuclides in the atmosphere and hydrosphere. The problems of determining radionuclides in the environment are discussed, including sampling, sample preparation, separation and concentration methods and the choice of a method for measuring radioactivity and identifying radionuclides. The analysis of various objects is described as examples. For students of radiochemical specialties, students of continuing education courses, as well as ecologists, geochemists and other specialists related to environmental protection.