Abstract: A continuous process for producing polymethyl methacrylate (PMMA) or its copolymer comprises precooling a monomeric feedstock consisting of methyl methacrylate (MMA) or a mixture of MMA and up to 10 mol % of a highly thermal radical-forming monomer, forcing the feedstock into a reactor wherein a preceding charge is being circulated under pressure, instantaneously mixing the whole charge and cooling it by dint of the sensible heat of the monomeric feedstock, while thoroughly mixing the hot radicals, thus effecting the polymerization within a short time period, continuously taking out from the reactor the polymerization product and unreacted monomer or monomers being circulatingly mixed, at a polymerization product proportion of 50% by weight or less, conducting the mixture, while preheating it, into a vacuum vessel, removing therein the remaining monomer or monomers by evaporation, and then recovering the polymerization product.