In the third edition of the Biomedical Engineering Handbook (Physiology of Thermal Signals), also republished in this edition, we introduced the reader to skin thermal properties in response to stress, regulation of skin blood ow for heat transfers, modeling equations, and objective thermography [1]. e objective thermography explored the eciency of heat transport in the hand-reduced blood ow, nerve block and laser Doppler mapping, and sports medicine injury applications. Most of the work in this current publication on thermal signals builds on that foundation of information. However, before we go into further detail on the use of IR thermography, it is important to review some basic principles in thermal physiology.