The stromal compartment of mesenchymal tissues is thought to harbor stem cells that display extensive proliferative capacity and multilineage potential. Stromal stem cells offer a potentially large therapeutic potential in the field of regenerative medicine. Adipose tissue contains a large number of stromal stem cells, is relatively easy to obtain in large quantities, and thus constitutes a very convenient source of stromal stem cells. Importantly, the number of stem cells obtained is compatible with extensive analyses of the cells in an uncultured, freshly isolated, form. This chapter describes procedures for isolating millions of highly purified stromal stem cells from human adipose tissue and methods of establishing polyclonal and monoclonal cultures of adipose tissue-derived stem cells.