From one of the world's leading experts on the history of energy, a rigorous examination of the transitions that structure our modern world--and the environmental reckoning that will mark its success or failure. What makes the modern world work? The answer to this deceptively simple question lies in four "grand transitions" of civilization--in populations, agriculture, energy, and economics--which have transformed the way we live. Societies that have undergone all four transitions emerge into an era of radically different population dynamics, food surpluses (and waste), abundant energy use, and expanding economic opportunities. Simultaneously, in other parts of the world, hundreds of millions remain largely untouched by these developments.