This first part of this chapter looks at the worldwide burden of gastric cancer at the beginning of the 21st century and summarises available population-based routine data that describes the variation in incidence of the disease in relation to age, sex, geography and time period. Consideration is also given to the differences in the descriptive epidemiology of gastric cancer arising in the proximal cardia region of the stomach. In the second part of the chapter, a brief review of the main identified environmental risk factors is conducted drawing, where available, on published systematic literature overviews and meta-analyses. Evidence relating the aetiology of gastric cancer to Helicobacter pylori infection, dietary factors, smoking, occupation, physical activity and anthropometry is presented.