The chemical interaction of tritium with various materials has been studied. The chemical state of tritium resting in materials depended on their chemical and physical conditions. The state of tritium can be classified into four categories, chemically bounded tritium, molecularly trapped tritium, tritium trapped as atomic state, and tritium localized in a special part. These chemical states in or on materials controlled the diffusivity of tritium in them and release from their surfaces. The chemical properties of materials mainly affect the resting state of tritium, but in some cases, the effects of physical properties are more important than those of the chemical ones.