Photopolymer materials have been widely used in some advanced industries owing to their practicability, low-cost, and ecological advantage. One of the key components of these photopolymer materials is a molecule that releases acidic species upon a photon trigger (known as Photo-acid generators, PAGs). Recently, PAGs have attracted much attention with novel technologies such as near-infrared CTP imaging, 3D printing, and EUV lithography, and are required to have various functions and sophisticated features. This review article summarizes recent advances in the molecular design and function of PAGs, which are required to respond to the increasing applications of the photopolymer materials in advanced industries.