Abstract: A process for the bleaching of cellulosic fibres comprising the steps of (a) providing a water supply; (b) adding hydrogen peroxide to the stabilised water supply to form a hydrogen peroxide solution; (c) adjusting the pH of the hydrogen peroxide solution by adding alkali; mixing the pH adjusted solution resulting from step (c) to allow complete formation of perhydroxyl ion; (e) adding a carboxylic acid anhydride compound to the solution resulting from step (d); (f) mixing the solution resulting from step (e) to allow complete formation of percarboxylic acid to give a dilute solution of percarboxylic acid; and (g) contacting the solution with a suspension of cellulosic fibres.