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It is an essential subject for coordination polymerization to achieve highly selective polymerization of conjugated dienes. As an emerging kind of homogeneous catalyst, rare-earth metal complexes bearing metallocene or multidentate non-metallocene ligands have become gradually attractive over the past ten years and more. The major emphasis of this review will be these rare-earth metal complexes and the effect of various conditions on the selectivity and activity of polymerization, including the Lewis acidity and ionic radii of central metal, the geometry of ligand, the temperature of polymerization, the species of co-catalyst and solvent. Moreover, the study of active species which initiate the polymerization is particularly concerned. By generalizing the relationship between the factor and the mechanism of polymerization, it is hoped to give an inspiration to catalyst designer and the researchers of coordinate polymerization.