This book examines the previously hidden and unpublished submissions made to the Irish Boundary Commission in 1924-25, offering a rare glimpse into a pivotal moment in Irish and British history. Based on meticulous research conducted at the National Archives in London, it examines the original submissions from 585 witnesses and 58 groups and public bodies during public hearings in Enniskillen, Armagh, Omagh, Derry, and Rostrevor. The Boundary Commission, established under Article 12 of the 1921 Anglo-Irish Treaty, faced numerous challenges, including civil unrest, political upheaval, and legal uncertainties, which delayed its work. The book explores key concepts such as the political dynamics of the time, the obstructionist policies of the Northern Ireland Government, and the impact of the Commissions recommendations. It also addresses critical questions about the legitimacy and consequences of the Commissions decisions, which were ultimately rejected by all parties involved in the Tripartite Agreement of December 1925. 2025 marks the finalisation of the geographical and political boundaries of the British and Irish states, a milestone often overshadowed by other historical events. An essential read for scholars, historians, and anyone interested in the intricate political landscape of early twentieth-century Ireland and Britain, this book provides a comprehensive understanding of the Boundary Commissions work and its lasting impact on both nations.