Fundamental organometallic reactions such as insertion and elimination and reactions of coordinated ligands are described. Cis-insertion and -elimination reactions generally require prior- and posterior-coordination of substrates to the vacant site of the transition metal complex, respectively. β-Hydrogen elimination of late transition metal complexes is very fast and frequently observed in the decomposition processes of organotransition metal species. On the other hand, external direct attack of nucleophiles toward coordinated substrates such as alkenes takes place in coordinatively saturated complexes. Chemical properties of substrates greatly changed by coordination, which is controllable by the ancillary spectator ligands and metals employed.