There is a persistent difference between development trajectories spanning the extremes of highly energy intensive (e.g. the United States) to highly energy efficient (e.g. Japan). The concept of “path dependency,” discussed further below, helps to explain these differences in energy use patterns among countries and regions even at comparable levels of income. The first is characterized by the emergence of steam power relying on coal that helped to overcome the constraints of preindustrial energy systems including the limited availability of mechanical power, low-energy densities, and the lack of ubiquitous and cheap transport systems (see also Landes, 1969). The second energy technology transition is characterized by the displacement of the previously dominating coal-based steam technology cluster by electricity (drives, light) and petroleum-based technologies (automobiles, aircraft, petrochemicals). This second transition is far from completed: some two billion still lack access to modern energy services provided by electric appliances and end-use devices (Johansson et al.,