Stereospecific polymerization of α-olefin and diene hydrocarbons in the presence of catalysts of a new type proposed by Ziegler and Natta is a significant discovery of the twentieth century in the chemistry of macromolecular compounds. Heterogeneous Ziegler-Natta catalysts involving Ti and V trichlorides in combination with organoaluminum compounds have been widely used for nearly 30 years in commercial stereospecific polymerization of a number of o-olefins (propylene, hexene-l,4-methyl-pentene-1, etc.) and dienes (butadiene, isoprene, etc.). However, despite the great success achieved in practical implementation of the processes there isnocommon point of viewsofar and broad discussions are still under way as to the mechanism of polymerization and stereoregulation in the presence of the above catalysts.