For the first time in domestic literature, this book systematically presents the concepts of biology, as well as the cellular and molecular foundations of the unique organ in animal organisms — brown adipose tissue (BAT). The uniqueness of BAT lies in its ability to generate heat through a specific mechanism involving uncoupling protein 1 (UCP1), which acts as a form of physiological work regulated by neuroendocrine processes, much like any other bodily function. Through BAT, small homeotherms maintain the temperature of vital structures in cold conditions, while heterotherms utilize it to emerge from hibernation. Under certain circumstances, BAT transforms excess nutrients into heat, protecting the animal from excessive obesity. Consequently, BAT with UCP1 and other members of the uncoupling protein family expressed in different tissues emerge as promising effectors and regulators for pharmacogenetic research aimed at protecting humans from obesity. This book is essential for specialists in ecological and comparative physiology and biochemistry, particularly those focused on the regulation of homeostasis, energy metabolism, and the challenges of obesity.