Functional imaging has many potential uses in cancer: as a predictive biomarker, for directing radiotherapy or targeted systemic therapy and in assessment of response. However, these have to date found limited use clinically. The investigation of both established imaging methods (perfusion CT and MRI, FMISO- and FDG-PET) and novel functional imaging techniques (CEST and oxygen-enhanced MRI) through longitudinal imaging studies of patients undergoing radiotherapy will be presented. Comparison with histopathological assessment and the potential to combine imaging with genetic data to provide a tailored management plan for patients with cancer will be discussed