To answer the most important questions of our age, we must understand size. Neither bacteria nor empires are immune to its laws. Measuring it is challenging, especially where complex systems like economies are concerned, yet mastering it offers rich rewards: the rise of the West, for example, was a direct result of ever more accurate and standardized measurements. Using the interdisciplinary approach that has won him a wide readership, Smil draws upon history, earth science, psychology, art, and more to offer fresh insight into some of our biggest challenges, including income inequality, the spread of infectious disease, and the uneven impacts of climate change. Size explains the regularities--and peculiarities--of the key processes shaping life (from microbes to whales), the Earth (from asteroids to volcanic eruptions), technical advances (from architecture to transportation), and societies and economies (from cities to wages). We also learn the rules governing beauty, why a biosphere needs diversity, why bigger animals need proportionately less food, and why people in hotter climates have longer legs.