Abstract
The detailed understanding of adult tissue stem cells has significance for both regenerative medicine and oncology. This perspective will discuss how major advances in our ability to identify and monitor these cells, which include genetic lineage tracing, FACS purification, and robust in vitro clonogenic assays, have changed our view of their roles in many organs. Label retention and quiescence are no longer considered obligatory stem cell features. Furthermore, some tissues have more than one type of stem cell, each used in only particular situations of regenerative stress. Thus, there is no "one size fits all" adult tissue stem cell paradigm.