It has been more than six years since France reintroduced controls at its internal borders, thus derogating from Schengen’s ordinary rules. A new border regime has emerged from this situation, one characterized by frequent reports of migrants’ rights violations. Combining legal ethnography at the French-Italian border and legal theory, this article explores the notion of “legal margin” to understand what happens between the border and the territory. This concept shows that the borderline affects how legal norms are applied within the territory next to it. It further unfolds through two ideas. Firstly, the maintenance of legal indeterminacies by the State updates and reinforces in an original way a fiction of a‑territoriality—people apprehended near the border are considered as if they were not in the territory—which places migrants outside the protective dimension of the law. Secondly, the regime of admission (the refusal of entry) is applied without the corresponding detention procedure (the waiting zone), thus allowing for what appears to be extralegal detention practices. The concept of margin seeks to enable legal theory to grasp what transpires in the ambiguity of the territorial space near the borderline and further explain exclusionary bordering processes.