Think of a biological cell as a tiny programmable device that happens to be alive, and you have the basic idea behind an emerging field called synthetic biology. Instead of trying to unravel the complexities of natural biological systems, “synthetic biologists” ultimately want to build highly predictable, simple living cells from scratch, using off-the-shelf parts. No one has done that just yet, but a growing number of scientists and engineers are now taking the first steps toward manufacturing life-forms to order.