Over the past several years, interest and activity regarding the use of heat to treat human malignancies has grown very rapidly. Laboratory studies with cells and animals have established the potential of hyperthermia, used alone, or in combination with radiation or drugs, for improvement of the therapeutic ratio in cancer therapy. A growing body of clinical data suggests that hyperthermia, employed as an adjuvant and perhaps, as a primary therapeutic modality, can often effect rapid and substantial tumor regression while causing only relatively modest changes in adjacent normal tissues. Given the clinical observations to date and the rationale provided by biological and physiological laboratory investigations, the current, prodigious growth of clinical utilization of hyperthermia in surgical, medical and especially radiation oncology is not difficult to comprehend. However, the development of clinical hyperthermia as a safe, effective and quantitative cancer modality will depend critically on the extent to which the physics and physiology of local, regional and whole body heating of human tissue are understood and properly incorporated into the planning and administration of thermotherapy. Whatever its promise, ultimately, the value of hyperthermia as a clinical tool will be governed, and perhaps limited by the physical aspects of power deposition, heat transfer and thermometry in vivo. This book discusses this important topic in depth.