Stem cells are relatively immature or undifferentiated cells that have been found to take up residence within a variety of organs, including the lungs or arise in more distant sites (particularly the bone marrow) in even more undifferentiated forms. Their role is not yet fully understood, but there is some evidence that these cells can participate in the reparative process following an injury. The observation that stem cells derived from one’s own body-autologous stem cells-might possess the ability to repair injured tissues has given hope that stem cells may be used to restore normal function to severely damaged organs, including the lungs. What is not yet understood is which cells are most appropriate for this purpose, or how to direct those cells to repair and restore normal function, particularly in organ as complex as the lungs.