The book, written by a prominent Soviet radiochemist, corresponding member of the USSR Academy of Sciences Viktor Mikhailovich Vdovenko, is devoted to the main issues of modern radiochemistry in the light of recent research. The history of the development of domestic radiochemistry is briefly considered. A significant place is given to general issues of theoretical radiochemistry (coprecipitation, co-crystallization, extraction, the state of radioactive elements in solutions, etc.). The monograph outlines the physicochemical properties of radioactive elements, as well as some applied issues: the scientific foundations of nuclear fuel chemistry, the use of radiochemistry in nuclear energy, oncology, etc. The book is intended for a wide range of research chemists and manufacturing engineers. It can serve as a teaching tool for students, graduate students and teachers of chemical departments of universities.