Much of the early interest in the economics of migration in developing countries focused on internal movements, especially the transfers of population from rural to urban settings. More recently attention has shifted toward international migration instead. This increased focus on international migration among analysts has been mirrored at the political level, heightened by changing realities: by the rise in immigration into the ‘more-developed’ regions, where the migrant stock now exceeds 10 percent of the population, including in large parts of Europe that traditionally saw net emigration; by the dramatic rise in recorded remittances in the last decade, reaching over $500 billion globally, of which more than $400 billion are going to the developing countries; by the expanding ‘brain drain’ from lower-to higher-income countries; and by security concerns surrounding international terrorism since 2001. Migration and economic development are mutually linked. Development may impact migration and vice versa, though the signs of causal links in both directions remain a matter of some dispute, as we shall see in the course of this volume. The various chapters chart the state of thinking on a number of key facets of the reciprocal links between migration and development, but also, in several instances, extend our frontiers of understanding with fresh evidence.