Gastritis, as a medical term, exists for the last 150 years, however, terminology and etiology (including the prognosis ) has changed. Gastritis related medical problems are in the focus of different sub-disciplines: internists, gastroenterologists, pathologists, immunologists, bacteriologists, genetics, biologists etc. After the publications by Marshall and Warren most of the clinicians accepted only the etiopathological role of Helicobacter pylori in the development of gastric and duodenal ulcer, as well as in the gastric cancer. This book presents chapters abou the history of gastritis terminology, animal models, epidemiology, new gastric mucosal endogenous defensive neural mechanism (capsaicin-sinsitive afferentation), different research and clinical methods applied to the background studies and the molecular pathology, biochemistry and genetics involved in the pathways from Helicobacter pylori infection to development of gastric cancer. Intended audience of this book are internists, gastroenterologists, pathologists, bacteriologists, pharmacologists, genetics, biologists, immunologists and other interested researchers.