An esterification process particularly for the preparation of rosin esters, polyesters and polymeric esters wherein aliphatic or aromatic carboxylic acids are reacted with appropriate alcohols in the presence of catalytic amounts of a mixture of a calcium hydroxyaryl phosphonate and an organosilicon heterocycle, the presence of said mixture serving to reduce the time necessary for complete esterification and to provide esters with increased oxidation stability and better color.