Multiple tissues can serve as a source of adult or somatic stem cells. Some of these tissues are available at only one point in the lifecycle, such as the umbilical cord, Wharton’s jelly, and placenta. In contrast, others are available throughout life and these include adipose tissue, bone marrow, and skeletal muscle. This chapter focuses on the latter three tissues due to their availability and utility for autologous and allogeneic transplantation. While none of these tissues yields a “perfect” stem cell, they do exhibit some of the following ideal properties: Abundant, accessible, and replenishable tissue source Multiple lineage differentiation potential Nontumorigenic Suitable for both autologous and allogeneic transplant Capable of retaining the desired properties after long-term storage Available in quantities of billions of cells Low immunogenicity Limited donor to donor variability Simple and reproducible isolation procedure