This book explains how UFOs work. It solves essential mysteries of UFO behavior that have been well-documented and unsolved for over fifty years. How is this possible? Very simple. The Center of UFO Studies (CUFOS) has for 30 years been accumulating a searchable database of UFO eyewitness reports. To date they number 209,000. To my knowledge no one has taken a serious look at these reports. I now have. All the conclusions in the book come directly from interpreting the eye witness reports. The basic conclusions were an inevitable consequence of applying standard physics principles to the reports. The fundamental revelation, that UFOs possess gravitationally negative mass, is an inescapable consequence of the fact that UFOs sometimes "levitate" people and cars. Gravitationally negative mass, when spun at high speed, allows UFOs to negate inertia. This fact suddenly throws the whole field of UFO behavior open. Now essentially all the activities of UFO can be understood. They can not only be qualitatively understood, but they can be calculated and predicted in detail. We do the calculations in the book and provide diagrams. We not only explain how UFOs kill inertia, but how they float in gravity, why they do zig-zag motions instead of smooth turns, why the sometimes exhibit "falling leaf" motion, how they propel themselves, and why they sometimes levitate objects. We explain the famous EM effects of car engines and headlights dying near UFOs, and why they do not create sonic booms at supersonic speed.