Brexit has intensified discussion of the border on the island of Ireland. One thing that both the Belfast/Good Friday Agreement (GFA 1998) and membership of the EU did was to take the hard edges off this issue by normalising movement, as well as promoting the idea of transnational institutions and the concept of multiple identities. Brexit, however, has re-opened in a new way the debate on partition, the existence of two jurisdictions on the island and the nature of that relationship. Harmonious North-South relations are a necessity for continuing peace and developing prosperity and the practical implementation of the peace Agreement. Brexit presents a series of threats and dangers to productive practical relations between the jurisdictions in the years ahead. It also carries with it a real risk to the relative ‘constitutional flexibility’ that was developing on the island.