THE PURPOSE of this book is to provide some basic psychiatric information about human hostility. It is also a call to the relevant sciences and to intelligent men and women everywhere to turn their attention to the world's most important and urgent danger: man's hostility to man, in the hope of helping to handle, control and alleviate the great suffering it creates. As this is written, the newspapers report that plans for a rocket trip to the moon are being discussed, that a scientist has devised a reasonable and practical way to travel to Mars and back. What was unthinkable yesterday becomes tomorrow's reality. The fact that great strides are daily being made in the understanding of human nature rarely makes headlines. But it is true that the dream of man maturing fully, living peacefully with his fellow men, and achieving his real nature of goodness and strength is now as much within our reach theoretically as is the dream of space travel. What makes criminals and great men, what makes the loftiest achievements of the human spirit and what makes the destruction, chaos and unutterable bestiality and misery of war—this is now known. To apply such knowledge is a vast and enormously difficult task in human engineering, but it is only a practical task. To show that this is so and to focus attention upon it is the goal of this book.