The diagnosis of H. pylori infection is based on methods requiring gastric biopsies performed during endoscopy (histology, culture, rapid urease test, PCR) or on non-invasive methods (serology, 13C urea breath test, stool antigen test). Histology is routinely performed on gastric biopsies, also allowing the description and the classification of the gastric inflammatory mucosal lesions associated with H. pylori. The rapid urease test is less sensitive but specific. It can be done by the gastroenterologist himself, mainly when a duodenal ulcer is found at endoscopy,and may be followed by histological testing in case of a negative result. The culture of biopsies may be helpful in determining in vitro patterns of antimicrobial resistance and sensitivity in planning second line treatment for a patient after eradication failure. Non-invasive methods are not appropriate for determining the underlying disease, which may be associated with H. pylori infection. Serological tests are widely available and cheap, and may be helpful-in screening populations or in confirming the presence H. pylori infection in case of equivocal results of the other diagnostic methods due to bleeding ulcers, antibiotic and/or antisecretory treatments. The 13C urea breath test is the most accurate method in patients irrespective of age. Stool antigen testing is a promising method because its diagnostic performances approach those obtained with urea breath test. This technique is easy to perform, and its accuracy may be improved by the use of monoclonal antibodies recently proposed for capturing H. pylori antigen in stool specimen. The eradication control is recommended at least 4 weeks after the end of the eradication treatment or at least 2 weeks after antisecretory treatment to obtain high sensitive results. If endoscopic control is necessary, a biopsy culture with antibiotic testing is recommended in combination with histology, because of the actual development of antibiotic resistances. Looking for H. pylori virulence markers remains a promising research topic but is not yet recommended in routine practice.