Book excerpt: The Irish border is a manifestation of the relationship between Britain and Ireland. When that relationship has been tense, we have seen the worst effects at the Irish border in the form of violence, controls and barriers. When the relationship has been good, the Irish border has become - to all intents and purposes - open, invisible and criss-crossed with connections. Throughout its short existence, the symbolism of the border has remained just as important as its practical impact. With the UK’s exit from the European Union, the challenge of managing the Irish border as a source and a symbol of British-Irish difference became an international concern. The solution found in the UK-EU Withdrawal Agreement gives the Irish border a globally unique status. A century after partition, and as we enter the post-Brexit era, this book considers what we should know and do about this highly complex and ever-contested boundary line.