Stem cells help to create new cells in existing healthy tissues, and may help repair tissues in areas that are injured or damaged. They are the basis for the specific cell types that make up each organ in the body. Stem cells are distinguished from other cells by a few important characteristics: they have the ability to self-renew; they have the ability to divide for a long period of time; and, under certain conditions, they can be induced to differentiate into specialized cells with distinct functions (phenotypes) including, but not limited to, cardiac cells, liver cells, fat cells, bone cells, cartilage cells, nerve cells, and connective tissue cells. The ability of cells to differentiate into a variety of other cells is termed multipotency. What scientists learn about controlling stem cell differentiation can become the basis for new treatments of many serious diseases and injuries.