Polyolefins represented by polyethylene (PE) and polypropylene (PP) are indispensable materials in our daily lives. TiCl3 catalysts, established by Ziegler and Natta in the 1950s, led to the births of the polyolefin industries. However, the activities and stereospecificities of the TiCl3 catalysts were so low that steps for removing catalyst residues and low stereoregular PP were needed in the production of PE and PP. Our discovery of MgCl2-supported TiCl4 catalysts led to more than 100 times higher activities and extremely high stereospecificities, which enabled us to dispense with the steps for the removals, meaning the process innovation. Furthermore, they narrowed the molecular weight and composition distributions of PE and PP, enabling us to control the polymer structures precisely and create such new products as very low density PE or heat-sealable film at low temperature. The typical example of the product innovations by the combination of the high stereospecificity and the narrowed composition distribution is high-performance impact copolymer used for an automobile bumper that used to be made of metal. These process and product innovations established these polyolefin industries. The latest MgCl2-supported TiCl4 catalyst is very close to perfect control of isotactic PP structure and is expected to bring about further innovations. (C) 2003 Wiley Periodicals, Inc.