In this comprehensive history of the Irish Boundary Commission, Paul Murray looks at British attempts from 1886 on to satisfy the Irish Nationalist demand for Home Rule; Ulster and British Unionist resistance to this demand; the 1920 partition of Ireland; and the 1921 Anglo-Irish Treaty, where the roots of the Irish Boundary Commission are found. The evidence presented at the Commission and the principles on which it based its decisions are analyzed against the background of evolving British views on the dangers posed for British and Unionist interests on both islands by a radical redrawing of the 1920 border.