In the final years of the twentieth century, emigres from mechanical and electrical engineering and computer science resolved that if the aim of biology was to understand life, then making life would yield better theories than experimentation. Sophia Roosth, a cultural anthropologist, takes us into the world of these self-named synthetic biologists who, she shows, advocate not experiment but manufacture, not reduction but construction, not analysis but synthesis. Roosth reveals how synthetic biologists make new living things in order to understand better how life works. What we see through her careful questioning is that the biological features, theories, and limits they fasten upon are determined circularly by their own experimental tactics. This is a story of broad interest, because the active, interested making of the synthetic biologists is endemic to the sciences of our time."