Migration is one of the most spectacular and controversial phenomena in the world economy, and also one of the least understood. In his new book, Paul Collier, professor of economics at Oxford University and a former director of Development Research at the World Bank, sets out to wrestle it to the ground and he gores some sacred cows in the process. Surprisingly for an economist, and a liberal one at that, he believes that migration should be carefully regulated and that this should be done for social rather than economic reasons.Current migration policy in rich countries, Collier suggests, reflects a toxic mix of “high emotion and little knowledge”. The right question for him is not whether migration is good or bad but how much is acceptable. “That is why migration cont