Triphenylsulfonium salts (TPS) have been formulated with polymers to make photosensitive systems for optical and optoelectronic applications. Photolysis of these salts generates strong acid which has been used in cross-linking reactions, deprotection reactions, and depolymerization reactions for photosensitive polymers, photodeformable polymers, and photo-doped conducting polymers. In addition, materials best described as polymeric sulfonium salts have been found to become conducting after photolysis. We have studied the photochemistry of TPS in polymer films and in solution. TPS photodecomposes by a mechanism that gives both in-cage recombination reactions and cage-escape products, and by reaction with solvent or polymer matrix. These products give cage/escape (C/E) ratios which are sensitive to the viscosity, rigidity, and polarity of the environment, and also the excited state from which the photochemistry occurs. Details of the reactivity and C/E ratios from photolysis of TPS salts in solution, have made it possible to determine their reactivity in polymers. In some cases the polymer behaves as a viscous solvent leading to high C/E ratios and in other systems the polymer excited state can sensitize the decomposition of TPS salts to give lower C/E ratios. Fluorescence studies on these polymers and quenching studies with TPS salts have helped to determine which excited states of the polymer and TPS salts are involved, and whether there is static or dynamic quenching in these systems. The photochemistry of model compounds for the polymeric sulfonium salts is also described.