Over 50% of the world population is chronically infected by the gastric pathogen, Helicobacter pylori, which is responsible for most peptic ulcer disease and is closely associated with adenocarcinoma of the stomach. Current therapies for peptic ulcer disease include antibiotic eradication of H. pylori infection. While effective, the high cost, difficulty of patient compliance with the treatment regimens, and risks of selection for resistant strains make these therapies impractical on a large scale. Studies of the pathogenesis of H. pylori have led to the identification of bacterial antigens as candidates for inclusion in novel vaccines against this disease. Both prophylactic and therapeutic vaccination have been demonstrated in animal models of Helicobacter infection. Preclinical evaluations of several antigens are at present under way and trials of vaccination in humans are planned.