Abstract: A method for the continuous manufacture of hydrocarbon resins starting from polymerizable insaturated hydrocarbons adapted to selectively obtain clear resins having well determined viscosities or softening points and to control the temperature of the polymerization reaction conducted in the presence of a Lewis acid as catalyst and recycling a fraction of the reaction mixture, due to the improvement comprising the steps of forming a close mixture of the catalyst and of the hydrocarbon fraction to be polymerized in a reactor, said mixture containing, by weight, from 0.05 to 0.8 part, and preferably from 0.1 to 0.