There is great interest in the use of heat, either alone or together with radiotherapy or chemotherapy, to treat cancer patients. In the paper, some of the physical techniques for heating tissues are discussed. These methods involve capacitive, inductive or radiative transfer of electromagnetic power to the tissue. Following a brief description of the interaction between tissues and electromagnetic fields in the spectral range 100 kHz–10 GHz, the advantages and\or disadvantages of each method are outlined. Throughout, emphasis is on clinical application.