Photorheological fluids (PRFs) are specialized materials that respond to light stimuli by undergoing changes in their rheological properties. These smart fluids have significant potential for integration into adaptive and smart technologies across various fields. This chapter aims to introduce fundamental concepts related to rheology. The discussion extends to the smart characteristics of PRFs, with a focus on the underlying mechanisms responsible for their viscosity modulation upon exposure to light. Furthermore, this chapter provides an overview of some applications where PRFs have demonstrated remarkable potential. These include their use in light-controlled lubrication systems, adaptive damping structures, and advanced sensing mechanisms. PRFs offer innovative solutions for industries requiring precise and contactless control of material properties.