A barium swallow, also known as an upper GI series or esophagography, is a diagnostic procedure that involves the use of X-ray imaging to examine the upper gastrointestinal (GI) tract, including the esophagus, stomach, and the first part of the small intestine (duodenum). The patient ingests a liquid containing barium sulfate, which coats the lining of the upper GI tract and makes it visible on X-ray images. This procedure helps in diagnosing conditions such as gastroesophageal reflux disease (GERD), ulcers, hiatal hernias, and other abnormalities.