The 1980s and 1990s saw a phase of increasing intergovernmental cooperation between European countries, culminating in Schengen and EU cooperation on immigration. This sharply exposed the divergence of migration control across European countries, triggering both ‘learning effects’ as countries adapted domestic legislation on asylum and borders, and ‘compensatory effects’ to mitigate the loss of internal Schengen border controls. Yet rather than leading to convergence, national systems of internal migration control remained surprisingly enduring. The chapter shows how the persistence of these divergences made arrangements on Schengen and free movement vulnerable to political shocks such as the 2015 refugee crisis and Brexit.