A process for the catalytic or non-catalytic esterification of acids or anhydrides with a mono-alcohol or a polyhydroxy compound which comprises the steps of adding the reagents to a reaction vessel to form a reaction mixture, and heating the reaction mixture and maintaining a pressure sufficient to obtain boiling of the reaction mixture thereby causing esterification and removing water as vapor while continuously mixing the reaction mixture in the reactor vessel such that at least about 2.5 to about 20 volumes of reaction mixture are internally recirculated per minute, whereby the rate of conversion is enhanced.