The new discoveries, the extraordinary dynamism in human stem cell (SC) research, and the great expectations of the benefits in clinical treatment of many diseases are on the edge of unparalleled advances in both: 1) the understanding of basic mechanisms of cell differentiation and development and 2) the translation from basic research to new clinical therapies. Human stem cells are obtained from different sources, such as embryo, fetal, and adult tissues, in vitro induction (iPS cells) or transdifferentiation. The evidence that these cells are pluripotent (or multipotent), meaning they have the ability to differentiate into all body tissues or tissues of the same lineage, raises the possibility that they could regenerate diseased or damaged tissue in diseases that until now have had no effective treatments. Human stem cell research and therapy raise important bioethical considerations because of the human nature of these cells and their peculiar characteristics. Here we discuss the bioethical aspects of basic human SC research and the conditions necessary for the translation of basic preclinical research into clinical use of SC.