This document discusses gastroesophageal reflux disease (GERD). It defines GERD as damage to the esophageal mucosa caused by reflux of gastric contents, as opposed to physiologic gastroesophageal reflux which does not cause symptoms or injury. The document covers epidemiology, pathophysiology including factors that increase or decrease lower esophageal sphincter pressure, clinical features of GERD, diagnostic testing, and classifications of GERD including NERD, erosive esophagitis, and Barrett's esophagus which is a precancerous condition.