We tend to think of political borders as exogenous artifacts that are imposed in a top-down manner by governments with imperial ambitions. And while this is true in some cases, there is a more significant case to be made for the alternative, where borders and jurisdictions are endogenous to the populations that draw them. A country's size and frontiers depend on the political and economic costs and benefits of sticking together or breaking up. Today we will have Enrico Spolaore, a leading economist in this research area, who will talk about countries' optimal size and why borders are drawn the way they are.