The report involves a review of the most important work on coordination chemistry carried out in the Soviet Union during this decade in the field of platinum metals, rare earth elements, actinides, as well as complex compounds of elements from various groups of the D. I. Mendeleev Periodic System. The results obtained on studying heteropolyacids and complexes with different new types of ligands, including complexons, are described, new data on coordination chemistry of organo-element compounds are reported, and the results of the study of complex compounds and of the nature of their chemical bonding as obtained by various physicochemical methods are characterized. Mention is made of studies concerned with explaining the phenomenon of complex formation in terms of the DI. Mendeleev Periodic Law. The report shows the development of coordination chemistry in the Soviet Union by its main research centres. Soon after its publication, the coordination theory developed by Werner gained considerable support in Russia. An important contribution in this respect was made by Chugaev, discoverer of the well-known reactions for nickel with dimethyiglyoxime, for osmium with thiourea, etc. Since 1904 he had been engaged in research on the chemistry of complex compounds, at first those of nickel and cobalt and later of various platinum metals. It was Chugaev who originated synthesis of a series of pentammine derivatives of platinum(iv), before unknown. He discovered the extraordinary strength of five-membered rings in complex compounds and the regularities of their formation1. In 1910 Chugaev published a monograph, On the Chemical Structure of Complex Compounds, in which he popularized and further developed Werner's ideas. The investigations of Chugaev and hi co-workers laid down the foundation for a large scientific school in the Soviet Union, which carries on extensive research on the chemistry of complex compounds of platinum and other elements. In 1926 (Cherniayev2, while studying nitrite complexes of platinum, discovered the trans-effect, which proved to be of great importance for the further development of the chemistry of complex compounds. Gel'man3 discovered a strong trans-effect of unsaturated organic molecules of the ethylene and acetylene type, which act as electron donors in the formation of coordination compounds.