The Irish border proved one of the most difficult issues in the negotiations on the United Kingdom’s withdrawal from the European Union. A persistent point of contention since the partition of Ireland a hundred years ago, it had been put into abeyance by a combination of the historic Common Travel Area, the peace settlement in Northern Ireland and the EU Single Market, which had allowed the disappearance of physical structures. The final agreement leaves important areas of ambiguity but does represent a breach in the UK’s vision of Brexit and a single settlement for the whole of the United Kingdom. It represents the first time that the EU has permitted partial integration in the EU for a region of a non-Member State but the circumstances are such that it does not provide a precedent.