The only curative treatment for localised gastric cancer is surgical resection. However, survival outcomes post-surgery alone remain poor, particularly in those with node-positive disease with 5-year survival of approximately 30%. Therefore, additional perioperative treatment strategies such as radiotherapy and/or chemotherapy have been explored to improve survival outcomes. Early studies established the role of postoperative radiotherapy in improving locoregional control. However, there are now several adjuvant treatment options available, with many centres favouring perioperative chemotherapy. The delivery of radiotherapy in the postoperative setting can be challenging, thereby resulting in suboptimal patient compliance. Hence, the role of preoperative radiotherapy is currently being evaluated. This review focuses on and summarises the landmark clinical trials that have established the current role of radiation therapy in patients with resectable gastric and gastroesophageal adenocarcinoma, and highlights the potential for preoperative radiotherapy.