This chapter introduces electrophysiological and electrical principles that underlie deep brain stimulation (DBS), with the purpose of facilitating effective and efficient postoperative programming. In order to comprehensively explore the effects of DBS, the entire set of electrode configurations and stimulation parameters would have to be systematically tested. There is considerable evidence that DBS-related changes in neurotransmitters and neuromodulators are unlikely to fully explain the DBS mechanisms of action. The control of the stimulating current is quite different in constant-current versus constant-voltage devices. The electrical charge generated during the DBS pulse dissipates with distance from the electrode. The stimulation parameters and electrode configurations can be used to control the spatial extent and number of axons excited by the DBS pulse. Excessive stimulation can lead to tissue damage by several mechanisms. In addition, unbalanced charges can create other reactive chemical species that can cause tissue damage.