The migration debate is often harsh and polarised, oscillating from calls for more open borders to promises to build new fences, and contrasting the views of those who emphasise the advantages and benefits from migration flows with those who consider migrants to impose an unnecessary strain on hosting societies. This column introduces a new eBook that offers a brief summary of what economists have learnt about migration in several crucial areas of policymaking, and identifies most of the important questions that still remain to be answered.