This paper is focused on: (i) the recent developments in LED technology, allowing the design of novel and efficient light sources for the free radical and cationic photopolymerization of various monomers, the synthesis of interpenetrating polymer networks (IPNs) or thiol–ene photopolymerization; (ii) the existing and emerging applications in these areas; and (iii) the development of novel photoinitiators and photoinitiating systems specifically adapted for LED excitation.