Book excerpt: The UK's decision to leave the EU has opened up huge existential questions for Northern Ireland as it marks its centenary. Constitutional conflict in Northern Ireland had been regarded as largely resolved and settled, but Brexit has altered the wider constitutional framework within which the 1998 Good Friday Agreement is situated. With the question of Irish unity gaining renewed and sustained traction, and with trade, relationships and politics across "these islands" in a state of flux, Northern Ireland approaches a constitutional moment. Murphy and Evershed examine the factors, actors and dynamics that are most likely to be influential, and potentially transformative, in determining Northern Ireland's constitutional future. This book offers an assessment of how Brexit and its fallout may lead to constitutional upheaval, and a cautionary warning about the need to prepare for it.