Extensive investigation of the biological effects of therapeutic heating has led to translation and clinical use of energy-based thermal therapy technologies for cancer treatment. Current clinical applications of therapeutic heating include mild hyperthermia as an adjuvant to ionizing radiation therapy and/or chemotherapy, and thermal ablation for stand-alone treatment of unresectable tumors. This chapter reviews the biological rationale for thermal therapies, introduces the basic concepts of thermal dosimetry, provides an in-depth review of the various energy modalities that have been investigated for delivering thermal therapy, and describes the integration of thermal therapy delivery technologies with imaging systems.