This book examines the law and politics of the Protocol on Ireland/Northern Ireland, attached to the Withdrawal Agreement, which regulates the terms of Brexit. The Protocol on Ireland/Northern Ireland deals with the most complex issue which emerged during the withdrawal negotiations between the United Kingdom (UK) and the European Union (EU), namely how to avoid a hard border in the island of Ireland and preserve the peace process started in Northern Ireland with the 1998 Belfast Good Friday Agreement. To this end, the Protocol, which was agreed in its final form in October 2019, establishes a bespoke solution, notably by keeping Northern Ireland aligned to EU customs and internal market rules. Nevertheless, the operation of the Protocol, which has formally entered into force in January 2021, has stirred political controversies in the Unionist community in Northern Ireland, and caused diplomatic confrontation between the EU and the UK. The purpose of this book is therefore to provide the first interdisciplinary overview of the Protocol, shedding light on its context, content, and challenges. This book — which brings together contributions by leading legal scholars, political scientists, sociologists, and trade experts from Northern Ireland, Ireland, Great Britain, Europe, and the United States — provides a comprehensive and contextual assessment of the Protocol. It examines its setting, including constitutional trends in the UK and Ireland, focuses on its substantive clauses dealing with human rights and cross-border cooperation, as well as on those related to trade, and analyses its governance mechanisms, including democratic consent and safeguards.