Stem cell therapy holds promise for treating many incurable diseases by replacing damaged cells. There are various types of stem cells including embryonic, adult, and induced pluripotent stem cells. While embryonic stem cells can differentiate into any cell type, their use is controversial due to requiring embryo destruction. Alternative sources like adult stem cells and iPS cells do not have the same ethical issues but may have limitations. Stem cell research faces challenges like preventing immune rejection and tumor formation but continues to advance regenerative medicine.