Size is the most fundamental structural variable of the universe. 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. Grounded in history and drawing on the latest science, with much recourse to art and classic literature, 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 learn, for example, the rules behind beauty, why a biosphere needs diversity, how to predict the size of a country, why bigger animals need proportionately less food and how a particular level of wealth inequality is inherent. Is bigger better? Can something keep growing indefinitely, or be too big to fail? To answer any of the most important questions of our age, and secure our future, we must understand size. Vaclav Smil tackles a goliath subject and it is no exaggeration to say that this tour de force will change the way you look at absolutely everything.