This article empirically maps and compares types of knowledge produced about people on the move by the European border security apparatus. Exploring two complementary analytical moments, the article addresses the stabilization of power and contingent practices within such apparatuses. We argue, first, that analyzing classification schemas implemented in data systems used within the European apparatus can reveal assumptions and limitations about people on the move—what we call “scripts of alterity.” Second, the comparative mapping of scripts of alterity reveals a de facto division of labor between scales of governance that would otherwise be invisible in policy. Utilizing the new Ontology Explorer software method as well as discursive analysis, we identify four scripts of alterity, which materialize relations in data systems and are thus relatively stabilized. Third, we identify as “de-inscriptions” forms of resistance specific to scripts of alterity. These can still be contested and we account for three contingent practices of de-inscription from scripts of alterity by conducting ethnographic observation of data systems’ use. Finally, we summarize three contributions that the “scripts of alterity” concept makes to the science and technology studies and to the critical security studies literature on the securitization of cross-border mobility.