"If one ranks cities by population, the rank of a city is inversely related to its size, a well-documented phenomenon known as Zipf's Law. Further, the growth rate of a city's population is uncorrelated with its size, another well-known characteristic known as Gibrat's Law. In this paper, I show that both characteristics are true of countries as well as cities; the size distributions of cities and countries are similar. But theories that explain the size-distribution of cities do not obviously apply in explaining the size-distribution of countries. The similarity of city- and country-size distributions is an interesting riddle"--National Bureau of Economic Research web site.