Helicobacter pylori (H. pylori) is a Gram-negative bacterium able to colonize the gastric mucosa as well as gastric metaplastic areas of the duodenum, producing inflammation. The clinical outcome depends on sophisticated interactions between bacterial factors, such as the expression of determinants of virulence and pathogenicity, and host characteristics. The severity of inflammation, may then vary among different subjects, leading to the occurrence of different gastroduodenal diseases, ranging from chronic gastritis to gastric cancer and MALT-lymphoma, to some defined extragastric manifestations. Many diagnostic tests are available for the detection of H. pylori infection including noninvasive methods, such as serology, (13)C-urea breath test (UBT), and fecal antigen tests and invasive techniques, including a combined use of endoscopic biopsy-based methods, such as rapid urease testing, histology, culture, and molecular methods. UBT is a highly sensitive and specific and allows to diagnose the presence or absence of infection of H. pylori, through the oral administration of a solution containing urea labelled with the non-radioactive natural carbon 13. This review article analyzes microbiological and clinical features of H. pylori as well as the different diagnostic tests able to detect this bacterium with a special focus on UBT.