Helicobacter pylori (H. pylori) is a gram-negative bacteria infecting more than 50% of human population. H. pylori selectively colonizes gastric mucosa and represents the major cause of gastroduodenal pathologies, such as gastric ulcer, autoimmune gastritis, gastric cancer and B cell lymphoma of mucosa associated lymphoid tissue (MALT). In this review interplay between H. pylori and both innate and adaptive immune responses is discussed. The second part of this article presents current knowledge about the relationship between H. pylori infection and neoplasia.