In the mid-sixteenth century, England was a small country on the periphery of Europe with an economy less advanced than those of several of its continental neighbors. In 1851, the Great Exhibition both symbolized and displayed the technological and economic lead that Britain had then taken. A half-century later, however, there were only minor differences between the leading economies of Western Europe. To gain insight into both the long period during which Britain outpaced its neighbors and the decades when its lead evaporated, it is illuminating to focus on the energy supply. Energy is expended in all productive activities. The contrast between the limitations inherent to organic economies dependent on the annual round of plant photosynthesis for energy and the possibilities open to an economy able to make effective use of the vast quantity of energy available in coal measures is key both to the understanding of the lengthy period of Britain’s relative success and to its subsequent swift decline.