Chemoradiation therapy (CRT) is a standard treatment for various cancers, including squamous cell carcinoma of the head and neck, non-small cell lung cancer, and rectal cancer. Regarding the sequence of radiation therapy and chemotherapy, concurrent CRT has yielded superior clinical results. However, CRT causes an increase in acute and late toxicities, despite improving local control and survival rates. The introduction of high-precision radiation therapy such as intensity modulated radiation therapy and newly developed chemotherapeutic drugs or molecularly targeted agents may further improve clinical outcomes while keeping treatment-related toxicities at an acceptable level.