The article traces the process of solving the Northern Ireland border issue in the framework of Brexit talks between the UK and the EU. Both sides are in favor of maintaining an open border between the United Kingdom and the Republic of Ireland, in order not to break the Belfast Agreement of 1998 that established peace between Catholics and Protestants after three decades of the ethnic and religious conflict in Northern Ireland. The EU wants to keep Northern Ireland in the Customs Union after the end of the Brexit, but Theresa May’s government fears that it could threaten the future territorial integrity of the United Kingdom. In this difficult situation, both sides are trying to develop an effective mechanism to prevent establishing hard border control that could provoke rise of confrontation between Northern Ireland’s communities.