It has been estimated that half the world’s population carries H. pylori.Most infected people remain asymptomatic during their lifetime, and only about 15% develop gastroduodenal disorders. This implies near perfect adaptation to the niche and an ability to evade the human immune response. Of those infected, about 10% develop peptic ulceration, roughly 1% develop gastric adenocarcinoma and less than 0.1% MALT (mucosa-associated lymphoid tissue lymphoma. Infection with H pylori elicits a systemic, strong and polymorphic humoral immune response. CagA is the important pathologic marker with a high immunogenic response.The highest titers of cag A antibodies (more than 100 arbU/ml) in the study realised by Ilie et al in 2011, was found for resistance to first line therapy, bleeding gastroduodenal ulcers, NSAID negative and gastric cancer. We recommend verification of H. pylori eradication to cag A positive patients one month after completing the treatment. This book will raise the interest of gastroenterologists,general practitioners,microbiologists,immunologists and last but not least medical students.