Adjuvant and neoadjuvant therapeutic principles have in recent years received increasing attention in the management of patients with carcinoma of the upper gastrointestinal tract. A series of randomized prospective trials has demonstrated that adjuvant postoperative radiation or chemotherapy does not result in a convincing survival advantage after complete tumor resection in gastric or esophageal cancer. The available data on the role of neoadjuvant preoperative therapy in these patients as yet permit no conclusion. While neoadjuvant therapy may reduce the tumor mass in a substantial portion of patients, a series of randomized controlled trials has shown that, compared to primary resection, a multimodal approach does not result in a survival benefit in patients with loco-regional, i.e. potentially resectable, tumors. In contrast, in patients with locally advanced tumors, i.e. tumors for which complete removal with primary surgery appears unlikely, neoadjuvant therapy increases the chance for complete tumor resection on subsequent surgery. However, only patients with objective histopathologic response to preoperative therapy appear to benefit from this approach. Compared to preoperative chemotherapy alone, combined radio-chemotherapy increases the rate of response, particularly in squamous cell esophageal cancer, but may also increase postoperative morbidity and mortality. Neoadjuvant therapy should therefore currently only be performed in experienced centers within the context of prospective clinical trials. The identification of factors that would allow prediction of response to neoadjuvant or adjuvant therapy is the focus of ongoing studies.