Effective prevention and early diagnostic strategies are the most important public health interventions in gastric cancer, which remains a common malignancy worldwide. Preventive strategies require identification and understanding of environmental risk factors that lead to carcinogenesis. Helicobacter pylori (H. pylori) is the primary carcinogen as this ancient bacterium has a complex ability to interact with its human host. Smoking and salt are strong independent risk factors for gastric cancer whereas alcohol is only a risk when it is heavily consumed. Red meat and high fat increase the risk of gastric cancer however fresh fruits, vegetables (allium family) and certain micronutrients (selenium, vitamin C) reduce the risk, with evidence lacking for fish, coffee and tea. Foods that inhibit H. pylori viability, colonization and infection may reduce cancer risk. Obesity is increasingly recognized as a contributory factor in gastric cardia carcinogenesis. Therefore, modest daily physical activities can be protective against cancer. Foundry workers are at risk for developing gastric cancer with dust iron being an important cause. Other risk factors include Epstein-Barr virus (EBV), possibly JC virus and radiation but the effects of these are likely to remain small.