The political and economic landscape in Ireland, the US and the wider world changed during the 1930s moving de Valera and Roosevelt away from a belief in collective security, as represented by the League of Nations, and towards neutrality. This study provides a fresh perspective on the diplomatic relationship investigating the mechanics of its operation and the complex factors that influenced its practice. Irish diplomats in the US worked on behalf of their government to consolidate national legitimacy and independence from Britain while US diplomats in Ireland always considered great power exigencies. The US-British ‘special relationship’ was the most important factor in the US-Irish relationship and not the reverse as de Valera mistakenly believed which was the flaw in his US policy.