Civilization's advances during the twentieth century are closely bound with an unprecedented rise of energy consumption in general, and of hydrocarbons and electricity in particular. Substantial improvements of all key nineteenth-century energy techniques and introduction of new extraction and transportation means and new prime movers resulted in widespread diffusion of labor-saving and comfort-providing conversions and in substantially declining energy prices. Although modern societies could not exist without large and incessant flows of energy, there are no simple linear relationships between the inputs of fossil fuels and electricity and a nation's economic performance and social accomplishments. International comparisons show a variety of consumption patterns and a continuing large disparity between affluent and modernizing nations. The necessity of minimizing environmental impacts of energy use, particularly those with potentially worrisome global effects, is perhaps the greatest challenge resulting from the twentieth century's energy advances.