Barrett esophagus is a metaplastic condition that affects the lower esophagus and is a complication of gastroesophageal reflux disease (GERD). Under normal circumstances, the reflux of gastric contents into the esophagus is prevented by a complex barrier at the esophagogastric junction. Dysfunction of the lower esophageal sphincter and the presence of a hiatal hernia lead to failure of this barrier. Esophageal mucosal damage results from the chronic exposure of the esophageal mucosa to gastroduodenal contents and the lack of an effective mucosal defense. This article is an overview of the dysfunction of the esophagogastric junction that leads to GERD. The role of the contents of the reflux and that of Helicobacter pylori infection in the pathogenesis of Barrett esophagus are also summarized.