“About once a year, a car-size asteroid strikes the Earth … roughly every five thousand years, the Earth is struck by an asteroid as big as a football field.” And then there are the really big ones every few million years—the kind that can trigger a global disaster. (Think dinosaurs.) How do scientists understand the past and potential future impact of asteroids on earth, and calculate risk? It’s work that takes place on many fronts, from amateur meteorite hunters to geologists studying craters of long-ago impacts to asteroid hunters, both amateurs and professional scientists, monitoring space using telescopes on the ground and orbiting the earth. Each kind of research and monitoring plays an important part in understanding asteroids and identifying potentially hazardous asteroids. The men and women introduced here share their fascination with their work, as well as things some readers may find surprising. (e.g., “A lot of science is writing … You are always trying to convey what you’ve done or what you’re hoping to do.”). The inviting design includes ample color photographs and graphics, while a final chapter, “How to Save the World,” offers fascinating theories on how we might try to divert a potentially devastating asteroid from impact. (Age 10 and older)