This book offers a serious look at defending the planet in the event of an extra-terrestrial invasion. Travis Taylor, et al, have written the definitive book on the defense of earth against a potential alien incursion. Whatever your beliefs on the subject, the book serves as an important primer on the potential future of warfare on every level. It is tightly grounded in current day realities of war and extrapolates thoughtfully but closely about future potentials. It should be on the reading list of anyone who is serious about national security and the future of war. The authors carefully make their case from every angle beginning with the statistical probability of an alien invasion. Chapter two discusses possible weapons, tactics and strategies for defense. This is followed with a look at what might motivate such an attack. And finally, who should know about preparations for defense, what a first and subsequent responses should be, and how we should be preparing and funding our defense. All four authors bring an incredible amount of serious space science to these questions. Dr. Taylor has a variety of experiences working for the Department of Defense and NASA. Dr. Boan has been an active member of the space community for over a quarter of a century. Dr. Powell is a professor with specialties including space trajectories, attitude dynamics, and numerical analysis. Mr.