Gastroesophageal reflux is defined as the passage of stomach contents into the esophagus with or without accompanied regurgitation (spitting up) and vomiting. It is a normal physiologic process that occurs throughout the day in infants and less often in children and adolescents. Gastroesophageal reflux disease (GERD) is reflux that causes troublesome symptoms or leads to medical complications. The diagnoses of gastroesophageal reflux and GERD are based on the history and physical examination. Diagnostic tests, such as endoscopy, barium study, multiple intraluminal impedance, and pH monitoring, are reserved for when there are atypical symptoms, warning signs, doubts about the diagnosis, or suspected complications or treatment failure. In infants, most regurgitation resolves by 12 months of age and does not require treatment. Reflux in infants may be treated with body position changes while awake, lower-volume feedings, thickening agents (i.e., rice cereal), antiregurgitant formula, extensively hydrolyzed or amino acid formulas, and, in breastfed infants, eliminating cow's milk and eggs from the mother's diet. Lifestyle changes to treat reflux in children and adolescents include sleeping position changes; weight loss; and avoiding smoking, alcohol, and late evening meals. Histamine H2 receptor antagonists and proton pump inhibitors are the principal medical therapies for GERD. They are effective in infants, based on low-quality evidence, and in children and adolescents, based on low- to moderate-quality evidence. Surgical treatment is available, but should be considered only when medical therapy is unsuccessful or is not tolerated.