Stomach cancer is the fifth most common incident cancer worldwide and the third leading cause of cancer death. Almost half of the world’s cases occur in Asia, with 42% in China alone. Although the incidence and mortality rates from stomach cancer are decreasing, the global disease burden remains high. Moreover, the absolute number of cases continues to rise because of population aging. Adenocarcinomas comprise over 90% of gastric malignancies. The adenocarcinomas are further classified according to anatomic location (cardia vs. non-cardia), histology (e.g., intestinal or diffuse, signet ring or non-signet ring) and most recently by molecular classification. Adenocarcinomas in the body and antrum of the stomach are usually caused by chronic infection with Helicobacter pylori (H. pylori); the incidence of these tumors is decreasing worldwide. Cardia tumors have epidemiological characteristics more similar to those of esophageal adenocarcinoma; the incidence of these tumors is increasing, particularly in high-income Western countries.