The 2018 Japanese Gastric Cancer Treatment Guidelines (5th edition) were updated to reflect new evidence since their initial publication. The guidelines emphasize a structured approach to gastric cancer treatment, incorporating the latest clinical data and methodologies. Key revisions include aligning the staging system with the 15th edition of the Japanese Classification of Gastric Carcinoma and the 8th edition of the UICC TNM classification. The algorithm for standard clinical practices was revised, with major changes or unresolved issues linked to clinical questions. The splenic hilar lymph node (No. 10) was removed from the definition of D2 lymph node dissection in total gastrectomy, and recent surgical studies were integrated. The indication for endoscopic resection was revised, introducing the "eCura" classification to replace outdated terminology. Chemotherapy regimens for unresectable advanced or recurrent gastric cancer were classified into "recommended" and "conditionally recommended" categories, with evidence levels defined according to the MINDS manual. Clinical questions were extracted to guide recommendations in surgery, endoscopic resection, and chemotherapy. The guidelines also emphasize the importance of lymph node dissection, with D1, D1+, and D2 classifications based on the type of gastrectomy. The extent of gastric resection was defined, with total, distal, pylorus-preserving, and proximal gastrectomies outlined. The guidelines highlight the role of laparoscopic surgery for early-stage cancer and the importance of reconstruction methods after gastrectomy. Endoscopic resection methods, including EMR and ESD, were detailed, with curability classifications (eCuraA, B, C) to determine treatment options. Systemic chemotherapy for unresectable advanced/recurrent gastric cancer was outlined, with regimens classified based on evidence levels and clinical trial results. The guidelines also address the management of HER2-positive gastric cancer, with trastuzumab-containing regimens as the standard of care. Overall, the guidelines provide a comprehensive framework for the diagnosis, staging, and treatment of gastric cancer, emphasizing evidence-based practices and individualized patient care.The 2018 Japanese Gastric Cancer Treatment Guidelines (5th edition) were updated to reflect new evidence since their initial publication. The guidelines emphasize a structured approach to gastric cancer treatment, incorporating the latest clinical data and methodologies. Key revisions include aligning the staging system with the 15th edition of the Japanese Classification of Gastric Carcinoma and the 8th edition of the UICC TNM classification. The algorithm for standard clinical practices was revised, with major changes or unresolved issues linked to clinical questions. The splenic hilar lymph node (No. 10) was removed from the definition of D2 lymph node dissection in total gastrectomy, and recent surgical studies were integrated. The indication for endoscopic resection was revised, introducing the "eCura" classification to replace outdated terminology. Chemotherapy regimens for unresectable advanced or recurrent gastric cancer were classified into "recommended" and "conditionally recommended" categories, with evidence levels defined according to the MINDS manual. Clinical questions were extracted to guide recommendations in surgery, endoscopic resection, and chemotherapy. The guidelines also emphasize the importance of lymph node dissection, with D1, D1+, and D2 classifications based on the type of gastrectomy. The extent of gastric resection was defined, with total, distal, pylorus-preserving, and proximal gastrectomies outlined. The guidelines highlight the role of laparoscopic surgery for early-stage cancer and the importance of reconstruction methods after gastrectomy. Endoscopic resection methods, including EMR and ESD, were detailed, with curability classifications (eCuraA, B, C) to determine treatment options. Systemic chemotherapy for unresectable advanced/recurrent gastric cancer was outlined, with regimens classified based on evidence levels and clinical trial results. The guidelines also address the management of HER2-positive gastric cancer, with trastuzumab-containing regimens as the standard of care. Overall, the guidelines provide a comprehensive framework for the diagnosis, staging, and treatment of gastric cancer, emphasizing evidence-based practices and individualized patient care.