This article analyses the interaction and intersection between an EU policy instrument -INTERREG -and bottom-up mobilisation of cross-border groups on the Irish border. The analysis involves an exploration of the interaction between the planning and negotiation of the INTERREG III programme for the border area between the Republic of Ireland and Northern Ireland, the establishment of new political institutions arising from the Good Friday Agreement and the 'bottom-up' mobilisation of new territorial actors on the border. Given that the Irish border is a contested one, it offers a useful lens to study the role of the EU in sustaining or mediating political con ict. The ndings suggest that the EU, notably the Commission, plays an important role in altering the opportunity structure of domestic actors and in providing them with new policy models. However, the ability of sub-state actors to take advantage of the new political space depends on developments in domestic politics. Perspectives on European Politics and Society, 4:3 © Koninklijke Brill NV, Leiden, The Netherlands, 2003 promote co-operation between different territorial units and in some cases different jurisdictions. Increasingly, the EU provides the backdrop and context for cross-border co-operation as well. The EU's wide range of powers, particularly those arising from EU regulations and monetary policy have a major impact on the political economy of border regions. Programmes such as INTERREG, the Community Initiative speci cally designed for Europe's borderlands, provide nancial incentives and an institutional model for crossborder co-operation. The objective of this article is threefold: To analyse the interaction between the planning and negotiation of the INTERREG III programme for the border area between the Republic of Ireland and Northern Ireland; to analyse the establishment of new political institutions arising from the Good Friday Agreement; and to explore the 'bottom-up' mobilisation of cross border groups seeking an enhanced role in the deployment of INTERREG III monies. The analysis is developed in three sections. Section one analyses the signi cance of the Irish border, its contested nature, the emergence of a European role in promoting cross-border cooperation and the continuing obstacles to cooperation. Section two explores the dynamics of change in relation to the role of the European Commission, the establishment of new institutions following the Good Friday Agreement, and the bottom up mobilisation of crossborder groups. Section Three analyses the way in which these changes have played out in the development of the INTERREG III programme. 1There is an extensive literature on the impact of the EU on territorial politics in the member states and on the emergence of multileveled politics and governance in the Union. The focus is on federal or regionalised states. Considerably less attention has been given to the impact of the Union on territorial politics when the territorial units themselves are a matter of contention within and between...