SUMMARYHelicobacter pyloriinfection is now recognized as the major cause of chronic gastritis throughout the world. A fraction of infected persons develop peptic ulcer disease or gastric cancer, accounting for its clinical significance. The pathophysiology of this infection can be better understood by considering five central concepts—heterogeneity of strains, persistence of infection, immunological down‐regulation, physiological consequences and variability in outcome. Microbial, host and environmental factors must each contribute to the outcome variat