There is overwhelming evidence that Helicobacter pylori is the major cause of chronic active gastritis and that it may further predispose to peptic ulcers, of which there are several thousand cases in the US each year. The most severe clinical outcomes of H. pylori infection are mucosa-associated lymphoid tissue lymphoma and gastric cancer. Because of these findings, the implications for cancer aetiology are intriguing. This book, a volume in the Infectious Agents and Pathogenesis series, presents chapters by major researchers in the field, including Dr. Barry Marshall whose research was responsible for establishing the linking of gastric ulcers with the H. pylori bacterium.