 A short but up-to-date review on the role of dyes in the photo initiation processes of polymerization reactions is presented. Radical and cationic reactions are largely encountered in the radiation curing and the imaging areas for use in traditional coding applications as well as in high-tech sectors such as nanofabrication, computer-to-plate processing, laser-direct imaging, manufacture of optical elements, etc. Recent promising developments concerned with the introduction of the silo-radical chemistry that enhances the polymerization efficiency are also discussed. This article was authored by Christian Le, Jacques Lelavi, Xavier Alonas, and others.