The dynamics of charge motion in tumbling mills has been a challenging problem both experimentally and theoretically. The harsh environment within the mill precluded sophisticated sensors. On the other hand, first principle modeling of charge motion was only marginally successful since the motion involves hundreds of bodies colliding with each other. The numerical scheme known as discrete element method (DEM) is the fitting solution to this modeling problem. The three-dimensional (3D) discrete element modeling of tumbling mills is described first. The simulation results are verified against both still images of ball charge motion and power draft in experimental mills. The excellent agreement implies that the simple spring-dashpot collision model is adequate for this problem. The simulation scheme can be extended for studying the life cycle of the mill itself.