Publisher Summary This chapter discusses the general theory of tribology. The systems approach to tribology is not intended to replace more traditional analyses of friction and wear processes. Much of the information required for the portrayal of tribological phenomena from a systems standpoint can be obtained through conventional procedures of analysis. For instance, important variables such as force, velocity, temperature, chemical potential and the related variables stress, strain, work, power, heat flow and reaction rates can only be determined by standard methods. In the application of system analytical methods to a certain complex subject, systems analysis often takes the form of "model building", i.e., the representation of a system graphically or analytically in a manner which may permit the model to be used for a mathematical study of the systems performance.