Recently, according to increasing gastroesophageal reflux disease (GERD), the patients with Barrett's esophagus (BE) are increasing. Since Barrett have reported cases of esophageal ulcers surrounding by columnar epithelium, the various criteria of the BE have been proposed. In 1998, practice guidelines for BE were developed under the auspices of the American College of Gastroenterology. They proposed that BE was a chance in the esophageal epithelium of any length that can be recognized at endoscopy, and confirmed to have intestinal metaplasia by biopsy of the tubular esophagus and excludes intestinal metaplasia of the cardia. Endoscopically, BE is determined, when 'gastric-appearing mucosa' or apparent 'columnar lined esophagus' is evident proximal to the esophagogastric junction. Histologically, BE has double muscularis mucosae, and contains a mixture cell types; gastric-fundic type epithelium, junctional type epithelium, and specialized columnar epithelium (SCE). Especially SCE is distinctive features of BE, available for diagnosis. On the other hand, BE is premalignant condition for the adenocarcinoma of the esophagus, therefore the features of the BE are researched to prevent and find out earlier development of adenocarcinoma. In this review, we referred to the definition of BE with some topics.