Two historians and philosophers of science offer an essential primer on the meaning and limits of regeneration.   In punishment for his stealing fire, the Greek gods chained Prometheus to a rock, where every day an eagle plucked out his liver, and every night the liver regenerated. While Prometheus may be a figure of myth, scholars today ask whether ancient Greeks knew that the human liver does, in fact, have a special capacity to regenerate. Some organs and tissues can regenerate, while others cannot, and some organisms can regenerate more fully and more easily than others. Cut an earthworm in half, and two wiggly worms may confront you. Cut off the head of a hydra, and it may grow a new head. Cut off a human arm, and the human will be missing an arm. Why the differences? What are the limits of regeneration, and how, when, and why does it occur?   In this book, historians and philosophers of science Jane Maienschein and Kate MacCord explore biological regeneration, delving into a topic of increasing interest in light of regenerative medicine, new tools in developmental and neurobiology, and the urgent need to understand and repair damage to ecosystems brought on by climate change. Looking across scales, from germ, nerve, and stem cells to individual organisms and complex systems, this short and accessible introduction poses a range of deep and provocative questions: What conditions allow some damaged microbiomes to regenerate where others do not? Why are forests following a fire said to regenerate sometimes but not always? And in the face of climate change in the era called the Anthropocene, can the planet regenerate to become healthy again, or will the global ecosystem collapse?