Of all cancers, non-small cell lung cancer is one of the most commonly diagnosed and is the deadliest. With a dismissal survival rate even in the early stages of disease, investigations of adjuvant and neo-adjuvant therapy have not had much impact until the 21st century. Starting in 2004, several randomized trials have shown significant improvements in survival treating patients with stage II and III disease. Adjuvant chemotherapy remains controversial in patients with stage I disease, in which most trials have not demonstrated a survival advantage. Investigators are studying molecular and genetic factors, which may predict who might benefit most from adjuvant therapy. While adjuvant therapy is now standard, neo-adjuvant therapy either with chemotherapy alone or with concurrent chemotherapy and radiation has shown promise, but has yet to become a clear standard of care. Data are presented to support the standard use of adjuvant therapy in patients with stage II and III disease, as well as data supporting the use of neo-adjuvant therapy in selected patients with non-small cell lung cancer.