AbstractThis chapter discusses how the structure and properties of Helicobacter pylori lipopolysaccharides (LPS) are adapted and modelled to fit the environmental niche of this bacterium and the pathogenic consequences of these structures, focusing on the lipid A moiety and O-antigen of this molecule. The low immunological activity of H. pylori LPS, the fine structure and biosynthesis of H. pylori lipid A, and the relevance of low LPS and lipid A immunoactivities to H. pylori pathogenesis are described. The role of H. pylori-expressed Lewis antigens in gastric adaptation and modulation of the inflammatory response is discussed.