This chapter assesses the importance of cooperation across the Irish border for attempts to find a political accommodation in Northern Ireland. If historical precedents are any guide, consensus on the nature and scope of cross-border linkages is likely to be very difficult to achieve, perhaps even more difficult than the decommissioning of paramilitary arsenals. Some of the most controversial proposals in both the 1920 Government of Ireland Act and the 1973 Sunningdale Agreement were for the creation of Councils of Ireland to give institutional underpinning to the development of relationships between north and south. More recently the British and Irish governments have promoted collaboration between Northern Ireland and the Irish Republic in the Anglo-Irish Agreement (1985), the Downing Street Declaration (1993) and a Joint Framework for Agreement (1995).