On September 8, 2015, the Court of Justice of the European Union (Court) ruled [3] that it is lawful for the United Kingdom and Ireland to participate in the Schengen acquis in a limited manner. According to Articles 4 and 5 of the Schengen Protocol [4] (Protocol), the U.K. and Ireland can request to participate in measures developing the Schengen acquis, subject to approval by the Council. Neither country had exercised its option to participate in provisions on external border crossings. Spain initiated the proceedings before the Court to annul Article 19 of the Eurosur Regulation [5] (Regulation), which allowed for an ad hoc participation by the U.K. and Ireland in the European Border Surveillance System and a system of cooperation at the external EU borders through multilateral cooperation agreements that did not need the approval of the Council. According to Spain, this violated the procedure set out by the Protocol, as it allowed the U.K. and Ireland to take part in measures which they had declined to participate in. The Court rejected this argument, stating that Article 4 of the Protocol had “the objective of allowing Ireland and the United Kingdom to be placed, as regards certain provisions in force of the Schengen acquis, in a situation equivalent to that of the Member States participating in that acquis.” By contrast, “Article 19 of the Regulation allows the implementation of a limited form of cooperation between Ireland and the United Kingdom and one or several neighbouring Member States but cannot place Ireland or the United Kingdom in a situation equivalent to that of the other Member States.” The Court decided that these limited forms of cooperation did not amount to a “taking part” within the meaning of the Protocol and concluded the Article 19 of the Regulation is not incompatible with the scheme set out by the Protocol.