Synthetic biology can change the genetic material in viruses, bacteria, yeasts, plants, or animals to give them useful new characteristics. For example, integrating spider DNA makes a silkworm produce super strong, ultra-lightweight silk. The technology could help address challenges in areas such as medicine, agriculture, manufacturing, and the environment. This Science & Tech Spotlight describes some of the benefits of synthetic biology and the challenges ahead. For example, while it could be used to engineer living cells that treat disease from within the body, it could also be used to make bioweapons.