In When the World Closed Its Doors, Edward Alden and Laurie Trautman tell the story of how nearly every country in the world shut its borders to respond to an external threat during the COVID-19 pandemic. They detail the consequences of the COVID border restrictions and explain why governments used their harshest containment measures on those coming from outside. A sweeping overview of the re-bordering of the world after 2020, this synthetic, wide-angle view of a singular shock to the international systems of travel and migration will be necessary reading for anyone interested in international migration and border policy.