Abstract: In the mid of 1980 there has been a revolutionary development in the catalyst technology after the discovery of metallocene catalysts. Group 4 metallocenes and constrained geometry catalysts have been at the fore front of the developments. In the late 1990, these catalysts are growing in commercial operations. Metallocene and other transition metal complexes plays an important role as highly active catalysts for the polymerization of polymers especially polyolefins, styrene etc. Experimental studies on different parameters like catalyst activity, effects of operating conditions, cocatalysts etc. have been studied by the researchers. In this review, the past, present and future scenario of metallocene catalysts is highlighted.