Platinum group metal catalysis uses ruthenium, rhodium, palladium, osmium, iridium, or platinum as the regenerated catalytic center in a homogeneous or heterogeneous reaction. Molecular PGM catalysts operate through ligand-controlled organometallic steps such as oxidative addition, migratory insertion, β-hydride elimination, and reductive elimination. Heterogeneous PGM catalysts instead present metallic, oxidic, nanoparticle, single-atom, or supported sites at which reactants adsorb and undergo bond activation ^[1][2]. Accessible oxidation states, strong yet tunable substrate binding, and the ability to activate H–H, C–H, C–X, C=C, O–O, and related bonds are characteristic features of this catalyst family. The class is defined by the identity and turnover of the metal, not by a single reaction mechanism. It excludes stoichiometric use of PGM compounds and processes in which a PGM is only a support or spectator. PGM catalysis is narrower than noble-metal catalysis, which can also include gold and silver, and distinct from base-metal catalysis.