The applications of mathematical simulations of tissue temperature distributions in hyperthermia treatments are discussed in terms of four areas, comparative, prospective, concurrent, and retrospective thermal dosimetry. These four aspects of thermal dosimetry cover the range of hyperthermia applications of interest to clinicians, from comparative evaluation of competitive heating modalities to individual treatment planning, through feedback control during a treatment and, finally, to posttreatment therapy evaluation. Mathematical simulations of hyperthermia treatments can play a significant role in each of these areas.