Endoscopic assessment of the esophagus for the presence or absence of gastroesophageal reflux disease (GERD) as well as the assessment of its severity is crucial to formulating decisions about the patient's management and prognosis. Therefore, a validated tool is required to ensure agreement among different endoscopists. The Los Angeles classification system of GERD is by far the most widely used system to describe the endoscopic appearance of reflux esophagitis and grade its severity.1 This article is part of an expert video encyclopedia.