Vagal nerve stimulation is a neurosurgical procedure consisting of implantation of an impulse generator battery with leads placed into the vagus nerve in the neck. This procedure was FDA approved for epilepsy in the 1990s and is commonly performed as an outpatient surgery. The mechanism of action is not well understood; however it is increasingly recognized that electrical stimulation of the vagus nerve may impact other organ systems in the body including the immune and gastrointestinal systems. Concrete characterization of the peripheral effects of VNS in human gut microbiome and immune systems will: (1) elucidate peripheral mechanism of action of chronic VNS therapy, (2) identify peripheral preoperative biomarker of VNS efficacy, and (3) create a foundation for research investigating new GM and IM-related disease indications for VNS. The primary objective of this study is to characterize the pre- and post-operative oral and gut microbiome of patients implanted with vagal nerve stimulator (VNS) for epilepsy. Secondary objectives of this study include: (1) to characterize the pre-operative and post-operative immune profile of patients undergoing VNS implantation for epilepsy, (2) to elucidate whether oral and/or gut microbiota changes are related to VNS efficacy for epilepsy and (3) identification of a biomarker predicting VNS efficacy.