UV‐radiation curing has become a well accepted technology which has found its main applications in the coating industry, the graphic arts and microelectronics. The liquid to solid phase change proceeds within a fraction of a second on intense illumination at ambient temperature. The kinetics of such ultrafast polymerization have been followed in situ by real‐time infrared spectroscopy. This technique proved well suited to assess the performance of the various constituents of a UV‐curable formulation (photoinitiator, monomer, functionalized oligomer) from measurements of the actual polymerization rate and of the final cure extent. The photopolymerization of both radical‐type (acrylates) and cationic type (epoxides, vinyl ethers) monomers has been examined, as well as that of monomer blends. Interpenetrating polymer networks have been synthetized by photocrosslinking of a hybrid acrylate/epoxide system which generates a hard and scratch‐resistant polymer material.