The Anglo-Irish Treaty of December 1921 led to the creation of an independent Irish state, but also a devastating Civil War that defined Irish politics for decades. Divisive as it proved to be, the signing of the Treaty on 6 December 1921 is a key milestone in modern Irish history. This lecture, based on the Irish National Archive’s landmark centenary exhibition on the negotiation of the Treaty negotiations, explores how it came into being, what it created, and the legacies it left behind.