Governing transit migration is an imperative for Europe. A record 1.3 million refugees applied for asylum in the European Union (EU) in 2015. Their number dropped in 2017 to 650,000 (Eurostat 2018) and return migration increased, but transit migration continues to affect the lives of millions trapped in mobility and immobility. Remarkably little is known about how transit migration is governed at different scales, through which mechanisms, and how is it affected by the institutional capacities and political regimes of states in different regions. This project develops a novel theory to study these questions through a relational approach to polycentric governance. The project unravels configurations of relationships established between various actors implicated in the governance of transit migration, and illustrates these by regional comparisons from Southern Europe, Eastern Europe, the Balkans, the Middle East, and North Africa.