During the last two decades, radiotherapy has become an integral part of the multidisciplinary approach in the treatment of patients with colorectal cancer. Currently, radiotherapy is seen mainly as an adjuvant therapy, sometimes in combination with chemotherapy, in a pre- or postoperative setting. Adjuvant radiotherapy alone leads to a significant reduction of local recurrence rates, but an impact on survival is seen only in subset analyses. Combined modality treatment can reduce local recurrence rates even further, and can also reduce the rate of distant relapses and increase survival. The acute toxicity of combined modality is considerably higher. Local radiation can also be use as a component of organ conserving local treatment for selected early lesions. Radiotherapy has been an important palliative treatment modality, diminishing symptoms in cases of inoperable primary rectal cancers or pelvic recurrences. The timing of radiation, surgery and chemotherapy has been under evaluation for years. For patients with locally advanced primary or recurrent malignancies (unresectable due to fixation), the preferred sequence is pre-operative irradiation with or without chemotherapy, followed by surgical resection. For mobile resectable lesions, sequencing issues are being tested in phase III randomised trials.