Big Science, defined as in the introduction to this book as the combination of big organizations, big machines, and big politics, has its origin in the unprecedented mobilization of science and technology in the service of the state during World War II. These efforts produced the first nuclear weapons, among other important inventions, and from the perspective of politics they most of all showed the world that basic research could have the power to alter the course of history through politics and translated into military might. But scientifically, the wartime R&D efforts were also a continuing pursuit of knowledge, a recent step in a natural continuation of scientific developments, though under new political and organizational conditions. The wartime experience set the framework for postwar science policy in Europe and the United States, and produced Big Science.