Discrete element simulations have been carried out to explore micromechanics and macroscopic deformation behavior of granular shear zones. Such numerical experiments allow us to look inside deforming fault zones and identify controls on fault zone structure, mechanical strength, and rheology. To date, simulations have focused on steady-state deformation of two dimensional non-cohesive granular assemblages, but more recently include velocity-dependent and time-dependent boundary conditions and contact laws. These discrete numerical simulations have successfully captured many features and behaviors observed in natural shear zones in the field and lab. The results are summarized below.