Spontaneous generation is one of those wrong theories that clutter the basements of the biological sciences and that now look so very obviously wrong that it is hard to see how anyone could have taken them seriously in the first place. Why wouldn’t it occur to anyone that flies might be laying eggs that were too small for us to see? How simple would the crucial experiment be? What I have tried to do in much of my work is to turn this ‘obvious wrongness’ on its head—why, exactly, does it seem so obviously wrong?—and see what the new picture that emerges from that inquiry says about science and our belief in its results. By taking spontaneous generation seriously as a sophisticated and above all a well-supported idea, I try to breathe new life into a world where processes that we, today, can’t even really imagine as plausible, were instead vivid, clear, and their details were hotly (and fascinatingly) debated. The epistemological disjunction—for my own part it is sometimes akin to vertigo—that this inquiry produces can shed some startling new light on how and why we think the way we do about the sciences, their authority, and even the realness of the entities and laws that they affirm or deny.