Adipose tissue is composed primarily of adipocytes, cells that function to store energy in the form of lipid droplets. Additionally, pluripotent progenitor cells, called adipose-derived stem cells, can be identified in adipose tissue by the expression of markers such as Integrin family members, CD44, and ICAM-1/CD54. Like mesenchymal stem cells, multipotent adipose-derived stem cells have been shown to differentiate into cells of the mesodermal lineage including adipocytes, chondrocytes, osteoblasts, osteoclasts, and myoblasts in vitro. Other in vitro studies suggest that adipose-derived stem cells have additional plasticity and can transdifferentiate into cells of other germ layers such as hepatocytes and neuronal-like cells. However, these biological actions remain to be confirmed in vivo. Because of their plasticity and accessibility, adipose-derived stem cells are useful for studies of regenerative medicine.