Stem cell technology has emerged in the face of extraordinary advances for prevention, diagnosis and treatment of human diseases such as heart disease, diabetes, cancer and diseases of the nervous system, such as Parkinson’s disease and Alzheimer’s Disease (AD). It offers great promise for tissue regeneration, cell replacement and gene therapy, but clinical applications remain limited. Despite considerable ethical and practical barriers to their acceptance in the society, their potential in medicine is tantalising. There is a balance between the search for ways to regenerate bodies ravaged by age and disease on the one hand, with the need to ground these ideas in scientific fact and medical caution on the other. Stem cells are certainly exciting both as models of developmental biology and potential in human disease. Brain can be turned into blood, blood can be turned into brain, muscle, myocardium or liver and in some hands, bone marrow and neural stem cells can be turned into almost any type of cell. Such remarkable properties render it now feasible to contemplate isolating living healthy stem cells from the body, expanding them under cell culture conditions, combining them with biocompatible carrier molecules, directing their proliferation with growth factors and then transplanting them or their progeny into patients for clinical gain. In this way stem cells may, in future, be used to alleviate degenerative disorders, replace diseased or failing tissues with engineered substitutes and correct genetic disease. These living tissue substitutes may indeed overcome the drawbacks of classic transplantation and the limitations of standard treatments for degenerative disease, but their origins and potential are increasingly challenged by developments in science and medicine, politics and ethics.