Perioperative chemotherapy for gastric cancer is validated by two phase III studies. The impact of the preoperative neoadjuvant sequence is probably major in the benefit of this treatment. This chemotherapy increases the R0 resection without increasing either morbidity or mortality. Furthermore, it reduces local and systemic recurrence improving disease-free survival and overall survival. The drugs used are 5-FU or its oral prodrugs, platinum salts (cisplatin or oxaliplatin) and anthracyclines. The perioperative chemotherapy must be proposed to all patients with a T3 or N+ gastric adenocarcinoma. This requirement imposes a rigorous preoperative evaluation including thoraco-abdominal computed tomography and for all non-metastatic patients an echo-endoscopy with biopsies. For patients not receiving preoperative chemotherapy, multidisciplinary consultations have the choice between an adjuvant chemotherapy based on 5-FU validated by a meta-analysis or a postoperative radio-chemotherapy whose application is validated by this phase III study.