In the Book of Judges, the Gileadites use the word shibboleth to target and kill members of a closely related tribe, the Ephraimites, who cannot pronounce the initial shin phoneme. In modern European languages, shibboleth has come to mean a hard-to-falsify sign that winnows identities and establishes and confirms borders; it has also acquired the ancillary meanings of slogan or cliché. The semantic field of shibboleth thus seems keyed to the waning of the logos in an era of technical reproducibility—to the proliferation of technologies and practices of encryption, decryption, exclusion and inclusion that saturate modern life. In the context of an unending refugee crisis and a general displacement, monitoring and quarantining of populations within a global regime of technics, Paul Celan’s subtle yet fierce reorientation of shibboleth merits scrupulous reading. Building on Jacques Derrida’s Shibboleth: For Paul Celan, but following its own itinerary, this book interprets the episode in Judges together with texts by Celan, passages from William Faulkner’s Absalom! Absalom!, and Doris Salcedo’s 2007 installation Shibboleth at the Tate Modern, pursuing the track of a word to which no language can properly lay claim—a word that is both less and more than a word, that signifies both the epitome and the ruin of border control technology, and that thus, despite its violent role in the Biblical story, offers Celan a locus of poetico-political affirmation.