Facilitated glucose transport is the movement of glucose across cell membranes that is driven by the glucose concentration gradient but assisted (facilitated) by carrier proteins. It is energy-independent, and it is stereospecific in that only the D-glucose isomer is transported; the L-glucose isomer is excluded. This process occurs in all mammalian cells and is essential for the maintenance of whole-body glucose metabolism and energy balance. Currently, there are five established functional facilitative glucose transporters in mammalian cells, termed GLUT1, GLUT2, GLUT3, GLUT4, and GLUTx. Each of these transporters has distinct but overlapping tissue distributions, which underscore their specific physiologic function.