This chapter originates from the results published in the literature as a starting point for the thermodynamic analyses of the human body (from a cell to the human body). The authors that contributed to this section are too many, although the initials of this research group are in the publications by the earliest beginning of 2000. We must not forget one main author of the first area to have an adventure in the exergy analysis of the human body and built several points in which his work can be considered the change in focus from entropy to exergy in this field. From the model, it was possible to propose new results related to thermal comfort and body composition conducted by researchers of the group. The idea is to propose environments and dress codes to make it possible to change the air-conditioning temperatures to reduce energy consumption. There is even an energy policy program in Japan named Setsuden to decrease the energy consumption in offices. Another step from this research field is related to sports performance for runners, cyclists, and weight-lifting. The aim is to properly model the human body from the phenomenological point of view (power, heat, and mass transfer rate) and process optics (exergy analysis). Eventually, there are a few studies regarding hypothermia as a therapy after a cardio-respiratory event. Herein, there is a systematic organization of the models available in the literature to help readers understand the applications in the following chapters.