Recent theoretical studies on reactions of Ziegler-Natta types carried out in our laboratory will be reviewed, in which the structures of transition states as well as reactants and products have been optimized with the ab initio molecular orbital energy gradient method. Those studies cover the electronic mechanism of olefin insertion along the reaction coordinates by the localized molecular orbital centroids analysis and the role of cocatalysis for heterogeneous catalysis models. In addition the isotacticity  of propylene polymerization for heterogeneous catalysis has been studied in detail.