Facial aging was once thought to be the result of the relentless downward pull of gravity on skin and underlying fat. In turn, facial fat was believed to be a contiguous sheet of tissue. However, over the past four decades, a number of investigators have examined more closely the causes of facial aging, leading to a better understanding of age-related changes, and have confirmed and further explored the proposal by Gonzalez-Ulloa and Flores in 1965 that facial aging involves changes in muscle and bone, as well as skin and fat. Further, the recent work of Rohrich and Pessa (and other authors) has demonstrated that facial fat is not a sheet of tissue, but rather is compartmentalized throughout the face. This discovery has allowed the evolution of improved techniques for facial rejuvenation.