This chapter investigates the peculiar and striking relationship that the mythical figure of the vampire has always had with the interfacial objects. In particular, it explores the most popular and important media adjuncts of the mirror and the window in modern times, the printed page and the moving image screen. The vampire is a profoundly unsettled creature. Neither alive nor dead, definitively un-dead, it dramatises humanity's troubled sense of being vulnerably, temporarily, uniquely alive while the rest of the universe is either differently alive, inanimate, or dead. The vampire, in one tradition at least, requires invitation: the predator must be welcomed, permitted to cross the interface. This aspect of the folklore provides the titular, narrative and emotional core of John Ajvide Lindqvist's novel Let the Right One In and its cinematic adaptations by Tomas Alfredson and Matt Reeves.