Europe and the United States are spending billions on the fortification of borders to stop migrants deemed unwanted by the government. The questionable effectiveness of this policy and its disastrous, often deadly consequences for people on the move have been studied extensively. The political project of closing borders to racially stigmatized migrants has serious consequences not only for outsiders who want to get in, but also for the internal organization of the society that is responsible for governing those borders. Taken together, these social and normative consequences constitute what we call the “internalization of borders.” Borders reach out far into society and are felt not only by would-be migrants in the places where they are stuck. Societies in the Global North, too, are being adversely affected and harmed by restrictive border regimes and their internalizing effects. Yet, unlike the “externalization” of borders, their “internalization” has so far not been researched systematically. To address the gap, this Introduction proposes a conceptual framework of how to study border internalization. The other articles in the Forum will offer diverse case studies on the dark side of border internalization as well as on ways of countering it.