The promise to end free movement of EU citizens was a trump card for the campaign to leave the European Union. Unlike the economic and sovereignty arguments, the immigration argument was simple and undeniably true: the UK could not control immigration while it remained a member of the EU. Experts on both sides of the referendum debate agreed that leaving the EU would reduce migration. For many voters, that was a pretty compelling argument. Fast forward six years, and migration post-Brexit had hit a record high. Net migration was three times the pre-Brexit level. What happened? Why did EU exit fail so spectacularly to deliver on its clearest promise? This chapter argues that the post-Brexit immigration system broke its promise to reduce migration partly by accident and partly by design. The government made liberal choices on immigration policy and underestimated quite how many migrants would take them up. Hardly any of this was an inevitable consequence of Brexit. In an alternative universe, things could have looked very different.