This thesis explores the reconfiguration of the Irish border roles post the Good Friday Agreement (1998). Through the lens of cross border co-operation, it aims to capture the changing role of the border between the two jurisdictions on the island. A key concept is that borders are no longer merely linear demarcations between states: they play in sometimes ambiguous roles in societies. These roles are captured using four dimensions of borders: barrier, resource, bridge and symbol of identity. These roles are challenged by European integration, globalisation and post-modernist approaches. Locally, the Good Friday Agreement provided new impetus to transnational linkages. The thesis examines the changing context through the lens of cross border co-operation. The thesis identifies three main rationales for co-operation between Northern Ireland and the Republic of Ireland: 1) ethno-national rationale views borders as territorial demarcation of nation-states dividing communities and they act as symbol of identity; 2) the economic rationale understands the border mainly as creating transaction costs and limiting competitiveness; 3) the peace & reconciliation rationale pursues co-operation with a view to end the caging of the ethno-national to Northern Ireland. These rationales are examined alongside the supporting institutional structures and how the discourses are reflected in policy, language and practice, combined they uncover the discourse. The research combines quantitative and qualitative methods of data collection. The analysis applies a constructivist approach analysis. The findings are that the ethno-national discourse restricts the development of cross border linkages. The barrier and symbolic dimensions remain highly significant and fundamental changes are slow and limited. The economic discourse has successfully reduced the barrier dimension in favour of the resource and bridging dimensions. The peace & reconciliation discourse has been less successful in reconfiguring the borders barrier and symbolic dimensions for its rationale.