The purpose of this investigation is to demonstrate the safety and effectiveness of Lower Esophageal Sphincter (LES) Stimulation System in treating gastroesophageal reflux disease (GERD). This investigation is a multicenter, randomized, double-blind, sham-controlled study. After the implant procedure, subjects will be randomized to either the Treatment Group (immediate stimulation) or Control Group (delayed stimulation) for six months followed by an additional open-label phase in which all subjects will receive electrical stimulation. Subjects continue on stimulation treatment in an extended open-label follow-up phase through 5 years post-stimulation.