This book analyses how Brexit will fundamentally alter Northern Ireland's constitutional arrangements. It charts how the United Kingdom's efforts to withdraw from the EU threaten to unpick or undermine some of the fundamental tenets of Northern Ireland's peace process. As the outline of a Brexit settlement comes into focus, this book examines its potential impacts upon trade, citizenship and human rights in Northern Ireland, and the broader implications of special arrangements for Northern Ireland for the constitutions of Ireland and the United Kingdom.