The Brexit referendum and its aftermath placed Northern Ireland and the question of a United Ireland in the public eye. The constitutional question was successfully put on hold when the Belfast/Good Friday Agreement was reached in 1998. British-Irish Relations in the Twenty-First Century examines the impact of the Belfast/Good Friday Agreement and Brexit on Northern Ireland, and British-Irish relations, from 1998 to 2023, highlighting the Agreement's successes, but also its failures. Tannam explores the challenges posed by a possible referendum on a United Ireland and emphasises the need to implement the Agreement's three strands. In particular, the book argues that the governments' weak guardianship of the Agreement contributed to its limitations. Tannam concludes that a joint intergovernmental strategy will be needed to manage identity politics, especially given the possibility of a future referendum on a United Ireland.