In 2001, it was observed that the cardia region of the lumen of the stomach remained highly acidic after a meal and escaped the buffering effect of the food. This phenomenon was termed the acid pocket and is thought to explain why reflux symptoms occur after meals despite the buffering effect of food. This review describes the discovery of the acid pocket and our progress in understanding the intragastric physiology producing it, its exaggeration in hiatus hernia and role in reflux disease. The recent discovery that the acid pocket is attenuated in the Helicobacter pylori-infected population and the significance of this to the negative association between H. pylori and reflux disease and its complications is also addressed. Finally, the role of the acid pocket in providing protection from potentially pathogenic ingested microorganisms is discussed.