Gastric carcinoma is one of the commonly diagnosed malignancies and remains an important cause of mortality in the Western hemisphere. Various sequences of genetic alterations may be responsible for the development of gastric cancer, as there exist two histological types: well-differentiated or intestinal-type and poorly differentiated or diffuse-type gastric cancers. While new genetic findings open new perspectives on carcinogenesis and molecular biology of gastric cancer, they have not been widely applied in routine diagnostic procedures, classification systems, disease monitoring, or prognostic assessment. We discuss the mechanisms molecular pathology in relation to their potential clinical relevance.