Gastric cancer (GC) usually has an unfavorable prognosis: the five-year survival rate is 20–30% in most world regions. Timely diagnosis and prevention of risk factors may reduce mortality from GC. This review discusses the meta-analyses of 40 endogenous and exogenous factors associated with GC. GC is significantly associated with family history; dietary preferences (increased consumption of roast and smoked red meat, hot foods, pickles, salt (over 5–6 g/day), nitrates (over 20 mg/L drinking water); lifestyle (smoking, opium use, strong alcohol, beer, stress); some diseases including gastroesophageal reflux disease, diabetes mellitus, obesity, and autoimmune disorders; infections (Helicobacter pylori, human papillomavirus, Epstein-Barr virus); ionizing radiation, and professional hazards. Data suggesting associations between the risk of GC and the consumption of coffee, tea, high-fat foods, simple carbohydrates, folic acid, sleep duration, and blood cholesterol turned out to be conflicting due to the inconsistencies of the results between cohort and case-control studies. About 3% of all gastric cancers are linked to hereditary syndromes associated with pathogenic variants of CDH1, STK11, SMAD4, BMPR1A, TP53, MYH, APC, PTEN, ATM, BRCA1, and some other genes.