Acid-base catalysis is the acceleration of a chemical reaction by proton transfer to or from the substrate in the rate-determining or product-determining step, so that an acid, a base, or a pair of acidic and basic sites stabilizes the transition state relative to the uncatalyzed path ^[1][2]. In catalysis and oxidation chemistry the concept is bounded by that proton-transfer elementary step as the catalytic event, and it includes both specific catalysis (by H+ or OH− of the medium) and general catalysis (by buffer acids and bases that are present in the transition state). Essential features are a donor and an acceptor of the proton, a defined timing of proton transfer relative to heavy-atom motion, and regeneration of the acid and base so that they are not consumed. Bifunctional acid-base catalysts place the two sites in a single molecular architecture, as in designed organocatalysts for the direct aldol reaction, so that enolate formation and carbonyl activation occur in one assembly ^[3]. The same proton-transfer logic operates at enzymatic active sites, including ribozymes and glycosidases, where nucleophilic attack is coupled to general acid-base assistance ^[1][4]. The concept is distinguished from nucleophilic catalysis, in which the catalyst forms a covalent adduct with the substrate, and from Lewis-acid catalysis, in which activation occurs by coordination of an electron pair rather than by proton transfer.