As end-of-the-world scenarios go, an apocalyptic collision with anasteroid or comet is the new kid on the block, gaining respectability only inthe last decade of the 20th century with the realisation that the dinosaurs hadbeen wiped out by just such an impact. Now the science community is making up for lost time, withworldwide efforts to track the thousands of potentially hazardous near-Earthobjects, and plans for high-tech hardware that could deflect an incoming objectfrom a collision course - a procedure depicted, with little regard forscientific accuracy, in several Hollywood movies. Astrophysicist and science writer Andrew May disentanglesfact from fiction in this fast-moving and entertaining account, covering thenature and history of comets and asteroids, the reason why some orbits are morehazardous than others, the devastating local and global effects that an impactevent would produce, and - more optimistically - the way future space missionscould avert a catastrophe.