Stem cells (SC) are characterized by the ability of self renewal as well as specialization into different cell types. Stem cells are present in most organs, and can be isolated from adult tissue, embryonic tissue and can be created by a new technology named induced pluripotency. The three types of SC have different potentials in terms of advancing regenerative medicine, but also raise serious safety concerns that need to be addressed before SC can fulfill the expectations by being developed into new cures and treatments for a range of serious cell degenerative diseases.