Data on polysite phenomenon (distribution of active sites by kinetic activity and stereospecificity of action) in polymerization are analyzed. The examples of polysite phenomenon manifestation and assessment, and its connection with ion, ion-coordination and radical polymerization conditions for olefins and dienes are shown. Geometrical and electron structure of active sites in ion-coordination polymerization of dienes is considered and the relation between the structure, reactivity and stereospecificity of action of different site types is shown.