White and brown adipose tissues, both present to some degree in all mammals, represent counter actors in energy metabolism. One of the primary functions of white adipocytes is to store excess energy as lipid, which is then mobilized to other tissues in response to metabolic needs that arise in times of food shortage. White adipocyte physiology can be grouped into 3 main categories with potentially overlapping mechanisms: lipid metabolism, glucose metabolism, and endocrine functions. Brown adipocytes, on the other hand, use accumulated lipid from food primarily as a source for chemical energy that can then be released from the cell in the form of heat. Recently, new discoveries about the significance of brown fat have sparked interest in this organ as a potential tool in the fight against obesity in adult humans. A basic overview of the anatomy and physiology of adipose tissue, with particular emphasis on the differences between white and brown fat, is presented.