This book covers the topic of Earth's Planetary Defense. This is not for the purposes of repelling an alien invasion, although the military has probably thought of that. Any civilization that could reach us is undeniably more technological advanced. We are focused, however, on big chunks of rock that could cause massive damage, and end civilization as we know it. It has happened - ask the dinosaurs. Ocean impacts, and Earth is covered by 75% water, recall, could trigger massive Tsunamis.The National Science and Technology Council is on record as saying we are unprepared as a nation for a large asteroid impact event. The last impact of a object some 10 km in size, 66 million years ago, caused an "extinction event." A four meter asteroid enters the Earth's atmosphere about once a year. For seven meters, its 5 years. That size produces a Hiroshima-sized explosion. For 20 meter asteroids, its twice per century. We just had one in 2013. We have had a success rate of four asteroids detected before they hit Earth's surface. It's the ones we don't detect that should trouble us. That, and the fact we don't have a clue on what to do about it, if its detected.