Deep brain stimulation (DBS) is an effective clinical treatment for several medically refractory neurological disorders. However, even after decades of clinical success, explicit understanding of the response of neurons to applied electric fields remains limited, and scientific definition of the therapeutic mechanisms of DBS remains elusive. In addition, it is presently unclear which electrode designs and stimulation paradigms are optimal for maximal therapeutic benefit and minimal side-effects with DBS. Detailed computer modeling of DBS has emerged recently as a powerful technique to enhance our understanding of the effects of DBS and to create a virtual testing ground for new stimulation strategies. This chapter summarizes the fundamentals of neurostimulation modeling, presents some scientific contributions of computer models to the field of DBS, and demonstrates the application of DBS modeling tools to augment the clinical utility of DBS.