During the last two decades of the nineteenth century and the first decade of the twentieth century, a remarkable political experiment was undertaken in the way Great Britain ruled Ireland. A succession of enlightened Chief Secretaries sought to repair the damage done to Anglo-Irish relations by centuries of mismanagement and oppression through the passage of substantive reforms in the areas of land ownership, agriculture, education, local government and public works. These reforms were designed to enable Irishmen to enjoy the same rights and opportunities in landholing, politics and education as those enjoyed by Englishmen. As Irishmen responded with gratitude and affection for England, all threats to the Union would disappear. Such (in outline) was the philosophy underlying Constructive Unionism. This study reviews Irish history since the Norman invasion in order to discover whether such a policy was truly an innovation, or whether it represented a reversion to earlier English approaches to the governance of Ireland. The backgrounds and social and intellectual milieus of the principle participants in the drama are also considered in order to better understand the way in which the policy grew out of the interaction of a particular set of men (and women) with specific events. The policy itself is studied in detail in order to better understand the underlying aims of the policy, and what its framers intended that it should achieve. Finally, the collapse of the policy is considered together with the implications of that collapse for all parties to the debate over Ireland from Ulster Unionists across the spectrum to militant Nationalists.