Stem cells are undifferentiated cells capable of unlimited selfrenewal and the ability to differentiate into multiple tissue types. Stemcells can be derived from early human embryo, human tissues after birth,and fetal tissues. Stem cells hold great promise because they can be used totreat large number of patients with degenerative diseases, blood diseases,malignancies, and genetic disorders. Stem cell research and eventualtherapeutic use are governed by the fundamental ethical principles whichare autonomy, beneficence and non-maleficence, the principle of freedomof research, and the principle of justice. Derivation of stem cells from adultand fetal tissues seems to be morally accepted. However, derivation ofembryonic stem cell is accompanied from its beginning by intense ethical,religious, and political debates.