Stem cells are a unique class of cells defined by their ability to turn into numerous different cell types and divide indefinitely. Traditionally, stem cells can be classified into two categories: Somatic (adult) and Embryonic.  Adult stem cells are found in certain tissues of the body and are only able to become a few cell types. However, they serve the important role of replenishing dead or damaged adult cells. For instance, hematopoietic (blood) stem cells in your bone marrow continuously produce blood cells, while skin stem cells continuously replenish your skin. Embryonic stem cells, on the other hand, are only found at the very first stages of development, but are pluripotent, meaning they are able to become any of the cell types that make up the body.