Brexit has created deep economic, political and constitutional uncertainty and instability, and nowhere has this been experienced more acutely, or with more far-reaching effect, than in Northern Ireland. Already unstable and crisis-prone, Northern Ireland's post-Agreement settlement was radically disrupted by the UK's 2016 decision to leave the EU (Murphy 2018a; Hayward & Murphy 2018; Cochrane 2020; Murphy & Evershed 2021). That decision was the culmination of a process that began long before referendum day, and which will continue long after 31 January 2020 (the day the UK formally left the EU). Here, we are concerned with the key episodes which have so-far defined Northern Ireland's Brexit: the important and enduring ways in which, during the UK's exit from the EU, they impacted on Northern Ireland, and vice versa. These pivotal moments are narrated here and further developed throughout this book. This account of Northern Ireland's Brexit experience is a necessary precursor to a more sustained analysis in later chapters of the role of different agents in this process, and how the way it unfolded was determined by the strategic calculations (and miscalculations) and decisions (and mistakes) of different agents, and with what potential long-term political and constitutional consequences.

The description provided here is necessarily partial in both senses of the word – incomplete and subjective – and acknowledges, indeed argues, that Brexit's consequences continue to unfold in both intended and unintended ways. Foregrounding the impetus and motivation for the UK's EU referendum, and analysing its subsequent conduct through a Northern Ireland lens, provides an important context for understanding why the “Irish question” became such a contested and complex issue following the vote. This helps to account for why the Brexit negotiations became bogged down by a British position which had a fatal contradiction at its core: namely, a desire to leave both the EU's single market and customs union (i.e. the desire for a “hard” Brexit) and to simultaneously maintain an open border on the island of Ireland.