Gastric cancer is the second most common cause of cancer mortality worldwide. Although the incidence of gastric cancer has declined over the past century in the United States, it remains one of the most common gastrointestinal neoplasms, particularly in immigrants and the socio-economically deprived. Recent years have seen major advances in our understanding of the pathogenesis of gastric cancer (especially regarding the importance of Helicobacter pylori and its associated inflammatory response) and the emergence of adjuvant oncologic therapies of proven benefit for advanced cases, in addition to surgery. As for gastric adenocarcinoma, elucidation of the underlying biology and molecular pathogenesis has led to much progress in the management of two other malignant gastric neoplasms, gastrointestinal stromal tumors and marginal zone B-cell (“MALT) lymphomas. This monograph highlights these developments, presenting an updated overview of gastric cancer that will be of interest to all practicing gastroenterologists.