Cancer starts with a change in one single cell. This change may be initiated by external agents and genetic factors. Cancer is a leading cause of death worldwide and accounts for 7.6 million deaths (around 13% of all deaths) in 2008. Lung, stomach, liver, colon and breast cancer cause the most cancer deaths each year. In this review, different aspects of gastric cancer; including clinical, pathological characteristic of gastric cancer, etiology, incidence, risk factors, prevention and treatment are studied.