Stem cells are undifferentiated cells of a multicellular organism which can differentiate into specialised cells through the process of differentiation, and which can also give rise to more cells of the same type through the process of mitosis. There are two types of stem cells in mammals – the embryonic stem cells and the adult stem cells. The embryonic cells are those stem cells that are generated from the undifferentiated inner mass cells of an early-stage pre-implantation embryo known as a blastocyst. The embryonic stem cells have the potential to differentiate into any cell type and also the ability to propagate. Adult stem cells are the ones found throughout the body after development. They are found in tissues. These are the cells that replenish dying cells and renew damaged tissues.