The global problems relevant to the environment and energy are attracting attention, so that it is considered that the construction of efficient light-energy conversion devices serves as an important subject of the scientific research. Thus far, the interaction between photons and molecules has not received much attention in photochemistry. However, the creation of a progressive methodology that allows an increase in the excitation probability is necessary because the photochemical reaction begins with light absorption process. Namely, to create a low-carbon-emitting society by utilizing light energy, it is necessary to introduce the concept of “effective utilization of photons” to photochemistry. In this chapter, the significance of the development of photochemical reaction fields, in which make it possible to increase the interaction between photons and molecules, is described. Metallic nanostructures showing localized surface plasmon resonance are a promising approach for the development of photochemical reaction fields. As an outstanding feature of our photochemical reaction fields, we have verified two-photon photopolymerization of negative photoresists on the closely spaced gold nanoparticles irradiated by a weak incoherent light source. We also demonstrated the efficient plasmonic photoelectric conversion by near-infrared light using electrodes, in which gold nanoblocks were elaborately arrayed on the surface of a titanium dioxide single-crystal.