Interpenetrating polymer networks (IPNs) have been synthetized by light-induced cross-linking polymerization of a mixture of acrylate and epoxide monomers. The consumption of each monomer upon W-irradiation in the presence of radical and cationic-type photoinitiators was monitored in situ by real-time infrared spectroscopy. The acrylate monomer was shown to polymerize faster and more extensively than the epoxy monomer, which was further consumed upon storage of the sample in the dark, due to the living character of cationic polymerization. Curing experiments carried out in the presence of air and under air diffusion-free conditions indicate that the radical polymerization of the acrylate monomer is hardly affected by the oxygen inhibition effect,, while the cationic polymerization of the epoxy monomer is enhanced by the atmosphere humidity. The addition of a photosensitizer, like isopropylthioxanthone, was shown to speed up substantially the polymerization of the epoxide, with formation within seconds of two fully cured IPNs.