Abstract: The role of chemistry in the studies on tribology and tribochemistry is reviewed. The theoretical and engineering issues of chemistry nature in tribochemistry are summarized and elaborated. The formation mechanisms of tribochemical films are elucidated based on the attempted applications of the chemical hardness concept, the hard and soft acid and base (HSAB) principle and its derived rules, such as the bond valence matching rule and the Saville rule. The major topics for future studies of tribochemistry are suggested as well. It is supposed that the study on tribochemistry is currently transforming from focusing on the experimental investigation characterized by the reaction among traditional ferrous metals, petroleum-based lubricating oils, and S -, P -, and Cl -containing additives, to focusing on the virtualization, micro-electro- mechanical-systems and engineering.