The Brexit campaign to withdraw the United Kingdom (UK) from the European Union (EU) was driven primarily by opposition to immigration and the freedom of movement of EU workers to Britain. Consequently, a central focus of Brexit was the perceived need for bordering, that is, the strengthening of Britain’s borders as security barriers to prevent the movement of these unwanted outsiders to Britain. Such bordering has the potential to turn the tide against decades of debordering on the island of Ireland that was delivered by Europeanisation, the North South provisions of the Good Friday Agreement, and a wealth of cross-border cooperation initiatives. From an open Irish border vantage point this paper explores three Brexit bordering options: bordering the United Kingdom of Great Britain and Northern Ireland; bordering Britain; and bordering the isles of Britain and Ireland. The argument is that the least costly one is to confine Brexit bordering to the island of Great Britain.