This book reviews and discusses the main economic reasons for the existence of peaks and troughs in the spatial distribution of population and wealth. Ever since the beginning of the Industrial Revolution, what makes some countries rich and others poor has been a central question in economics and history (Landes, 2000; Helpman, 2004). In comparison, little attention has been paid to the reasons why some regions, or other subnational entities, are rich while others are not. Another long-neglected topic is the impact of distance on the diffusion of economic development within and across countries. In other words, behind the mystery of economic growth stands another mystery: why do some places fare better than others? Why is inequality found at all spatial scales, from the international and regional to the urban and local? Firms and people are not concentrated on the head of a pin, nor are they spread evenly over a featureless plane. On the contrary, they are distributed very un equally across localities, regions, and countries, generating contour lines that vary with time and place. As a result, economic activity within countries is concentrated in a fairly limited number of cities and regions. Furthermore, economic growth is and has always been geographically unequal, on all spatial scales. At the global scale, in 1980 the European Union (EU-15) accounted for 29 percent of world gross domestic product (GDP), the North American Free Trade Area (NAFTA) for 27 percent, and East Asia for 14 percent. These three blocs thus produced 70 percent of world GDP. Twenty years later, the share of the EU-15 had fallen to 25 percent, while that of NAFTA had increased to 35 percent and that of East Asia to 23 percent. Together, they accounted for 83 percent of world GDP in 2000. Sizable spatial differences also exist within countries and take the concrete form of large cities and regional agglomerations. For example, in 2008 the capital region of the Republic of Korea, which covers 11.8 percent of the country’s surface area and includes 48.6 percent of the population, produces 47.8 percent of Korea’s GDP. In France, the contrast is even greater: the metropolitan area of Paris, which accounts for 2.2 percent of the country’s area and 18.2 percent of its population, produces 28.3 percent of its GDP. Similarly, in Brazil, the world’s fifth-largest country in surface area, 33.9 percent of GDP is produced by 21.6 percent of the population in the state of Sao Paulo, which occupies only 2.9 percent of the country’s area.