Esophagitis in cats and dogs is a consequence of increased exposure of the esophageal mucosa to gastroduodenal reflux. Causes can include anesthesia-related reflux, frequent vomiting, or lodged foreign bodies. An exception is eosinophilic esophagitis, an emerging primary inflammatory disease of the esophagus with a presumed allergic etiology. Reflux esophagitis owing to lower esophageal sphincter incompetence is often suspected; a tentative diagnosis can be made by endoscopic assessment, wireless esophageal pH-monitoring, or histologic examination. Because it can be difficult to distinguish diet-responsive upper gastrointestinal disease from esophagitis, response to treatment with gastric acid suppressants is needed to confirm the tentative diagnosis.