The broad definition of a stem cell is a cell that has the ability to self-renew and differentiate into one or more specialized terminally differentiated cell types. It has become evident that stem cells persist in, and can be isolated from, many adult tissues. Adipose tissue has been shown to contain a population of cells that retain a high proliferation capacity in vitro and the ability to undergo extensive differentiation into multiple cell lineages. These cells are referred to as adipose stem cells and are biologically similar, although not identical, to mesenchymal stem cells derived from the bone marrow. Differentiation causes stem cells to adopt the pheno-typic, biochemical, and functional properties of more terminally differentiated cells. This chapter will provide investigators with some background on stem cells derived from adipose tissue and then provide details on adipose stem cell multilineage differentiation along osteogenic, adipogenic, chondrogenic, and neurogenic lineages.