This book, written by a Harvard physicist for people who remember some of their high school physics and are unfazed by numbers, provides quantitative answers to most of their questions about energy. It presents a whirlwind history of humans’ relationship with energy sources, which at first was mostly wood and brawn, with help from domesticated animals, wind, and water. All that changed when Abraham Darby discovered how to make coke from coal in 1709 and when, soon after, Thomas Newcomen invented the steam-driven pump. These two technical leaps ushered in the age of coal-generated steam power -- and the age of fossil-fuel dependency. McElroy’s book includes an extensive discussion of the physics and geology of coal, oil, and natural gas, along with useful chapters on nuclear energy, electricity, transportation, climate change, carbon capture, and ethanol (which, McElroy points out, will do nothing to mitigate climate change if it is made from corn but could be helpful if it could be made economically from cellulose). The book has a clearheaded discussion of a low-carbon energy future.