To measure the impact of the Collins legacy, I have identified a set of key indicators: (a) The continuing impact of Collins’ action on events. (b) The continuing influence of his political ideas. (c) The behaviour of his entourage and followers. (d) The extent to which he has been interpreted and re-interpreted, by whom and why. Following an opening chapter which analyses Collins’ career, I have applied the above indicators to the issues and policy questions that concerned him at the time of his death: Firstly, the conduct and conclusions of the Civil War. I examine the different views as to whether or not Collins would have sanctioned the executions and reprisals policy which bequeathed its own bitter legacy. Secondly, I examine the tensions within the National Army over its development - politically-motivated cadre, or a professional army subservient to the Irish electorate? While the former view has its advocates I argue that those who enforced the latter vision were following the direction set by Collins. Central to my thesis is the argument that Michael Collins, more than any of his leading Pro-Treaty allies or Anti-Treaty opponents, detested the partition of Ireland. I argue that the gap between Collins’ expectation and the Boundary Commission’s report was a major failure of his legacy. By contrast, I argue that his Pro-Treaty heirs made an important contribution to transforming imperial relationships in the direction of the “association of free states” envisaged by Collins where he signed the Treaty. I discuss the extent to which the record of the Cumann na nGaedheal governments of 1922-1932 was primarily a vindication of, or a departure from, Collins. I also test De Valera and Fianna Fail’s claim on Collins’ legacy. The thesis also examines the efforts to airbrush Collins from the official history, and the reasons behind his ‘come-back’ in recent years including analysis of the significance of Collins’ biographers. An appendix examines a Scottish connection in the circumstances surrounding his death.