A multiplicity of legal and political arrangements regulate the European Union's external borders. With borders representing the intersection between national and international law and politics, the EU also acquired some legal competences in this realm. The resulting triple set of rules coincides with the growing disaggregation of the classical functions of borders. This state of affairs generates legal and procedural uncertainties and results in a growing ambiguity and lack of transparency, in terms of competences and accountability. Due to the EU's concerns with transnational terrorism, and the growing securitization of migration, the EU's borders with the states of the Middle East and North Africa are particularly relevant in this regard, with the resulting uncertainties touching upon fundamental rights. This article discusses the conceptual starting point of the growing institutional, legal, and political complexity at the EU's southern borders, together with relevant aspects and developments, thus al...