Based on the motion of the grinding media in stirred media mills with disc stirrer different grinding mechanisms are possible: product particles can be stressed by grinding media which are accelerated from the stirrer shaft towards the grinding chamber wall (A), which are pressed against the chamber wall because of the centrifugal acceleration (B) and which move in tangential direction with high velocities and collide with grinding media with lower velocities (C). The importance of the three different grinding mechanisms can be determined by evaluating the respective stress intensity and the respective number of stress events per unit time. The theoretical investigations showed, that the product particles are broken mainly by stress mechanism C. This finding was confirmed by experimental investigations concerning the comminution of limestone in a stirred media mill.