Every day we draw in two thousand gallons of air -- and thousands of living things. From the ground to the stratosphere, the air teems with invisible life. This last biological frontier remains so mysterious that it took over two years for scientists to finally agree that the COVID pandemic was caused by an airborne virus. In this book, Zimmer leads us on an odyssey through the living atmosphere and through the history of its discovery. Travel to the tops of mountain glaciers, where Louis Pasteur caught germs from the air, and follow Amelia Earhart and Charles Lindbergh above the clouds, where they conducted groundbreaking experiments. We meet the forgotten pioneers of aerobiology including William and Mildred Wells, who tried for decades to warn the world about airborne infections, only to die in obscurity. Air-Borne chronicles gripping accounts of how the United States and the Soviet Union clandestinely built arsenals of airborne biological weapons designed to spread anthrax, smallpox, and an array of other pathogens. It also leaves readers looking at the world with new eyes -- as a place where the oceans and forests loft trillions of cells into the air, where microbes eat clouds, and where life soars thousands of miles on the wind.