The intervening decade since the first edition of Borders: A Very Short Introduction has witnessed a flurry of events that highlight the centrality of borders in political affairs. These include surges in migrant and refugee flows; renewed emphasis on traditional border security; tensions over maritime sovereignty; advances in cybersecurity and surveillance; expanded detention and deportation infrastructures; new transborder organizations; populist and nationalist sentiments; and protectionist and integrationist trade practices. This revised edition accounts for recent developments including Brexit, the 2015 migration crisis across Europe, efforts to build a US-Mexico border wall, demands for indigenous homelands, Russian cross-border incursions, and insurgencies and rebellions across much of North Africa and Southwest Asia.