Many people think of medical ultrasound as being used solely for clinical diagnosis, and they are unaware of its therapeutic potential unless they are sportsmen who have received ultrasound treatment for so tissue injuries. In fact, the use of therapeutic ultrasound predates its imaging applications. As ultrasound travels through tissues, a number of physical mechanisms take place. ese include thermal eects arising from energy absorption and mechanical eects that are caused by the passage of an acoustic pressure wave through tissue. Both these classes of mechanism can be harnessed for therapeutic benet. A range of biological responses may be sought from the bioeects achieved. For physiotherapy, where the goal is functional modication for therapeutic reasons, the changes may be reversible or irreversible. In cancer therapy, ultrasound may be used to induce temperatures in the hyperthermic range (43-50°C) for use in conjunction with radio or chemotherapy or may be used on its own to create thermally ablated volumes when the temperature is raised rapidly above 55°C, or, as in histotripsy and drug delivery, to induce cavitation. As will be discussed in the following section, the dierence between these regimes lies principally in the amount of power deposited in the tissue and the mode of delivery.