The First World War is a major event in world history and in Ireland’s history as well. This article demonstrates how myth, memory and history became intertwined in contemporary understandings of Irish participation in the conflict, as well as in subsequent scholarly writing. Through examples including recruitment statistics, policy decisions, the war at sea, memorialisation, unionism and Northern Ireland, and the Irish Revolution, this article demonstrates that a triangular relationship between myth, memory, and history has pervaded our understanding of the history of the war itself. A critical appreciation for how and when these phenomena intersect is therefore needed for a better understanding of Ireland and the First World War—and how we as historians continue to write its history today.