The current S3 guidelines on the diagnosis and treatment of gastric carcinoma including those of the esophagogastric junction describe optimal clinical practice based on a high level of evidence and expert consensus from different medical disciplines. Endoscopy and performance of multiple biopsies is the standard approach to detect malignant tumors in the upper gastrointestinal tract. Further diagnostic procedures are necessary to evaluate the tumor stage. With the exception of mucosal carcinomas, surgical therapy is the cornerstone of curative treatment in all potentially resectable stages. In locally advanced carcinomas perioperative chemotherapy should be carried out and in high-seated tumors preoperative radiochemotherapy might be an alternative option. Palliative surgical resection should be avoided in disseminated asymptomatic stages. In a palliative situation complications of the tumor should primarily be treated by interventional or conservative procedures.