Some parts of our bodies can repair themselves quite well after injury, but others don’t repair at all. We certainly can’t regrow a whole leg or arm, but some animals can regrow - or regenerate - whole body parts. Regeneration means the regrowth of a damaged or missing organ part from the remaining tissue. As adults, humans can regenerate some organs, such as the liver. If part of the liver is lost by disease or injury, the liver grows back to its original size, though not its original shape. And our skin is constantly being renewed and repaired. Unfortunately many other human tissues don’t regenerate, and a goal in regenerative medicine is to find ways to kick-start tissue regeneration in the body, or to engineer replacement tissues.