Helicobacter pylori is the first formally recognized bacterial carcinogen and is an important human pathogen that colonises the stomach of about half of the world's population. Helicobacter pylori is the major cause of gastritis and gastritis-associated diseases: gastric ulcer, duodenal ulcer, gastric cancer, and primary gastric B-cell lymphoma (MALT lymphoma). Treatment of H. pylori infection results in ulcer healing and can reduce the risk of gastric cancer development. The recognition of H. pylori has had a substantial effect on gastroenterological practice, since many untreatable gastroduodenal disorders resolved with the eradication of H. pylori. In this review, we focus on the epidemiological and clinical features, mechanisms of pathogenesis, diagnosis and on the treatment of H. pylori infection.