Migration governance is at all times, and in all places, a necessarily organisational process. What this means is that governance ‘actors’, meaning people working for organisations of varying types – such as national governments, international organisations and NGOs – and with starkly varying degrees of power, must address two basic and linked questions that confront all organisations: what is going on ‘out there’ and what should we do next? The result is that migration governance is necessarily based on judgements, perceptions, and understandings of international migration in its various forms, but these develop in the shadow of considerable uncertainty about the causes and effects of migration. In other words, how we think about the causes of migration affects how we design policies to influence migration, and these understandings vary considerably across the world.