The New York Times best-selling author on the source of great bounty—and now great peril—all over the world. Phosphorus has played a critical role in some of the most lethal substances on earth: firebombs, rat poison, nerve gas. But it’s also the key component of one of the most vital: fertilizer, which has sustained life for billions of people. In this major work of explanatory science and environmental journalism, Pulitzer Prize finalist Dan Egan investigates the past, present, and future of what has been called “the oil of our time.” He describes the race to mine it from the fabled guano islands to the far Pacific to the sand dunes of the Western Sahara. He reports on how our overreliance on phosphorus is today causing toxic “dead zones” in waterways from the Florida Everglades to the Mississippi River Basin to the Great Lakes and beyond. And he explores the alarming reality that diminishing access to phosphorus poses a threat to the food system worldwide—which risks rising conflict and even war.