A work regenerative chatter in plunge grinding is theoretically studied in this paper. A dynamic grinding force due to the penetrating volocity is derived from a simple basis of a constant volumetric grinding energy theorem for the work material. The contact behaviour between the surfaces of the grinding wheel and work is also included in the analysis and it is shown that each contact stiffness of the grinding wheel and work should be separately treated in the vibration system in plunge grinding. A new block diagram for the regenerative chatter in plunge grinding is introduced and the critical conditions for the chatter vibrations are discussed. The results obtained are as follows. The effects of a number of the grinding variables such as the structural dynamic stiffness, damping coefficient, the natural frequency, the volumetric grinding energy of the material, the plunge velocity, the diameter of the work and wheel, grinding width and the contact stiffness of the wheel and work, on the stability of the chatter are all calculated. The effects of the structural stiffness and the grinding width on the chatter are much different from the results expected in other investigations given by many researchers. The structural stiffness has only small effect on stabilizing the chatter at relatively large grinding width. The large grinding width may also cause to suppress the chatter.