Understanding what fat is and how it behaves is of paramount importance to understand the fat transfer procedure to sculpt any part of the body including the buttocks. Adipose tissue or fat tissue is composed of fat cells and a tissue called connective tissue that holds them in place. These fat cells contain lipids and this is what gives the fat cells the yellow color. Fat cells can grow as big as 120 microns as a person gains weight. To put this on perspective, a human hair is typically between 40 to 120 microns. In other words, fat cells can get pretty large. A large aggregate of fat cells with connective and its blood supply form two layers throughout the body. There is a superficial layer of fat cell with a well-organized structure and a deep layer with a less structured framework. Clinically, this is very important because the deep layer of fat contributes significantly to the thickness in areas where liposuction is performed. Fat cells behave in a very unique way depending on the metabolic demands of the body and also on the amount of body fat. Typically, an individual from 20-25 y/o age, the total fat content is about 15% for men and 25% for female. As a the person gets obese, the fat cells increase in size but can also increase in numbers. Based on the embryology, which is the science on how living organism grow, it has been determined that during the first year of life the amount of fat cells will triple and will also increase during adolescence. Then, it will reach a plateau and stay static for the rest of a person’s life as long as a critical threshold in fat cell size is not reached. Now, what happens after this fixed amount of fat is developed and stays static throughout life has evolved from a notion that we have a fixed number of fat cells throughout the life spam of an individual to the revolutionary theory that there are adiposite derived stem cell. These cells basically can transform into other cell types including fat. These adiposite stem cells have the ability to proliferate after transplantation and increase vessel formation. In other words, not only fat cells can increase in size, but they can also multiply from a common precursor depending on the physiological status of the body at any given time.