The emergence of strange new diseases is a frightening problem that seems to be getting worse. In this age of speedy travel, it threatens a worldwide pandemic. We hear news reports of Ebola, SARS, AIDS, and something called Hendra killing horses and people in Australia—but those reports miss the big truth that such phenomena are part of a single pattern. The bugs that transmit these diseases share one thing: they originate in wild animals and pass to humans by a process called spillover. David Quammen tracks this subject around the world. He recounts adventures in the field—netting bats in China, trapping monkeys in Bangladesh, stalking gorillas in the Congo—with the world’s leading disease scientists. In Spillover Quammen takes the reader along on this astonishing quest to learn how, where from, and why these diseases emerge, and he asks the terrifying question: What might the next big one be?