The history of the double-balloon endoscope from conception to development and practical application has been described. The theory itself is quite simple, and there were opinions doubting its practicality at the early stage of development.Double-balloon endoscopes, however, are commercially available now. They have been used widely, and their usefulness has been recognized. When development of the double-balloon endoscope was progressing, development of capsule endoscopes also was progressing. The authors often heard opinions that, since capsule endoscopes were expected to become commercially available in the near future, it was out-of-date to devise a method to insert an enteroscope into the small intestine. The authors, however, believed that if the use of capsule endoscopes spread, the necessity of an enteroscope that can reach the entire area in the small intestine would not disappear, but become even bigger. If any abnormal finding is detected by a capsule endoscope, the necessity of enteroscopy for a detailed examination increases. This is being proven at present.