Selenium and organoselenium compounds are used in a wide variety of scientific and technical fields. Many classical methods of converting selenium and its compounds take a long time (4-6 hours). One of the most effective methods of "green chemistry" is organic synthesis under microwave activation conditions, which in many cases significantly reduces the reaction time and, in some cases, eliminates the need for solvents. The book discusses an environmentally friendly chain of sequential transformations of dirty selenium into high-purity selenium dioxide, then into selenic acid esters, and the subsequent regeneration of high-purity selenium under microwave activation conditions.