Helicobacter pylori is the cause of chronic active gastritis. It is integral to the pathogenesis of peptic ulcer disease and is epidemiologically linked to gastric cancer and lymphoma. Helicobacter pylori can be detected through a variety of invasive (urease testing, culture, or histologic diagnosis of endoscopic biopsies) and noninvasive (urease breath tests, serologic tests) diagnostic tests. It is now appropriate to detect and eradicate H pylori in patients with a peptic ulcer as the natural history of peptic ulcer disease is then markedly improved. At this time, there is no role for H pylori eradication in the prevention of gastric cancer; however, this concept is being actively investigated. There is no indication to treat patients who have H pylori and nonulcer dyspepsia or gastritis because eradication does not reliably affect their symptoms. Current regimens for eradication include bismuth, antibiotics, and antisecretory agents. Complex and poorly tolerated regimens (triple therapy) may no longer be necessary, as simpler regimens (omeprazole and amoxicillin or clarithromycin) appear to be as effective and better tolerated.