Deep brain stimulation (DBS) represents a powerful clinical technology, but we are only beginning to understand the details of the interaction between the electrode(s) and the brain. This presentation will provide an overview of the latest advances in experimental and theoretical characterization of the electrode-tissue interface (ETI) for in vivo DBS electrodes. We use electrode impedance spectroscopy to guide development of equivalent circuit models of the ETI. We then perform microelectrode recordings of the in vivo voltage distribution generated by DBS to guide development of finite element models of the stimulation. These models are then used to predict the effects of stimulation on a patient-specific basis using magnetic resonance imaging data from the patient. Patient-specific models have progressed to the point of enabling the prospective prediction of stimulation parameter settings that rival the therapeutic benefit of settings selected by clinicians. In turn, scientific characterization of the ETI is clinically relevant and can assist in the optimization of clinical outcomes from DBS devices.