In this paper, various models of the milling process in frequent use are reviewed. They are classified in order of increasing sophistication and accuracy as (1) the Average Rigid Force Static Deflection Model, (2) the Instantaneous Rigid Force Model, (3) the Instantaneous Rigid Force, Static Deflection Model, (4) the Instantaneous Force With Static Deflection Feedback Model, and (5) the Regenerative Force, Dynamic Deflection Model. In each case, the validity, possible applications, and limitations of the model are discussed. In the final section, several applications of the Regenerative Force, Dynamic Deflection Model are used to illustrate the wide range of applicability of this model.