In addition to the electron-deficient nature of trivalent group 13 elements, Lewis acidity of group 13 metals can be greatly enhanced by changing a metal center from neutral to cationic, thus allowing for interesting and novel chemistry. However, there have been only a few examples of isolated cationic indium complexes since the first group 13 cationic metal complex reported in 1967. Furthermore, the reactivity of these complexes has remained largely unstudied. Hence, we have made an effort to develop a series of neutral indium complexes and explore their reactivities. Recently, in continuation of our work with the neutral indium complexes, I have developed cationic indium complexes supported by tridentate Schiff base ligand that possess unique catalytic properties such as the selective formation of spiro-orthoesters (SOEs) known as expanding monomers from functionalized epoxides and lactones, and direct double ring-opening polymerization of SOEs. In addition to the cationic indium complexes, neutral analogues are also found to have an ability to block copolymerize racemic lactide and methyl methacrylate for biocompatible amphiphilic block copolymers. In this talk, the development of neutral and cationic indium complexes and their catalytic activities will be discussed with promising experimental results and proposed mechanisms.