Helicobacter pylori (H. pylori) is a gram-negative bacterium which is responsible for a wide range of disorders of the stomach, from chronic gastritis to peptic ulcers to gastric cancer which, however, occurs in a lower percentage of subjects. The difference in the clinical course of infection seems to be correlated both to the typical pathogenicity of the bacterium and to factors related to the host. The reasons underlying these observations include differences in bacterial pathogenicity as well as in host susceptibility. Numerous studies published in the last year have provided new insights into H. pylori virulence factors, their interaction with the host and the relative consequences in the pathogenesis. In this review, we have set ourselves the target of summarising the latest progress made in understanding the molecular aspects of H. pylori infection of notable importance for the physician.