An emission behavior of molecules is one of the most attractive phenomena in the field of photochemistry. It is obvious that the emission behavior was affected by the surrounding environment such as a solvent. Especially, the chemical reaction field provided by host materials could modify the photochemical property of the guest molecule. For example, unique effects of host materials such as emission enhancement have been found out. In this review, the effect of host materials such as cavitand, zeolite, and clay on the emission property of guest molecules are described from the viewpoint of photochemistry.