An investigation of the photoinitiated cationic ring-opening polymerizations of various epoxy monomers was conducted using real-time infrared spectroscopy and optical pyrometry. Several types of behavior were observed and interpreted on the basis of the relative stabilities of the secondary and tertiary oxonium ion intermediates that are generated during the ring-opening polymerization of these monomers. Based on the mechanistic interpretations proposed, attempts were made to accelerate the photopolymerizations of epoxy monomers that undergo overall slow reaction as a result of the presence of an induction period. Three general methods were effective for the acceleration of the photopolymerizations of these and other epoxy monomers: (1) carrying out the photopolymerizations at higher temperatures, (2) copolymerization with more reactive monomers, and (3) the use of free radical photoinitiators.