The formation of densely crosslinked networks by chain crosslinking photopolymerization is discussed in relation to selected applications in the electronics industry. All of these applications make use of the high speed and of the latitude to meet other requirements by variation of the chemical structure of the monomers. The selection comprises: 1. The coating of optical fibers ; 2. The replication of optical discs; 3. The replication of aspherical lenses, used for laser read-out of these discs. Other important processes will only be mentioned briefly for the benefit of a discussion of more fundamental results that have been obtained during the study of the selected examples. These results relate to the crosslink density, the influence of light intensity on polymer structure, the relation between shrinkage and chemical conversion, a parallel with physical aging, kinetics during vitrification, the importance of chain transfer, the build-up of peroxides in photopolymers and computer simulation of network formation by crosslinking polymerization. This serves to illustrate the continuous interaction between development of applications and fundamental research.