Iridium catalyst development has not kept pace with other group 9 elements such as cobalt and rhodium. Until recently there was a problem with the stability of the iridium complex, but research activities have accelerated since the development of ligand stabilization. One of the first commercialization activities has been in a hydrogenation reaction where the iridium catalyst has shown high activity. Various studies are being carried out actively with future development for iridium catalytic reaction expected.