The Northern Ireland Good Friday Agreement (GFA) signed in 1998 has been presented by many, including those in Irish nationalist circles, as a sign of a post-national de-territorialisation of Irish national identity, made possible or even necessary by globalisation. Studying the discourses of the main Irish constitutional nationalist parties in both Northern Ireland and the Irish Republic, prior to and after the GFA, this article argues that this process is best understood instead as a dialectical unfolding of deterritorialising and reterritorialising trends. The first section analyses the concepts and theories of the de/reterritorialisation debate and proposes a theoretical framework through which the de/reterritorialisation of national identities might be understood. The second section sets the groundwork for the terms in which such a framework might be applied to the territorial claims advanced by the main Irish nationalist constitutional parties. Finally, the third section examines the complex history of competing claims over the importance of territory in both cultural and political Irish nationalist movements, Specific attention is given to debates over the GFA. It is concluded that Irish nationalism has long been divided on the status of its territorial ambitions. As such recent literature on de/reterritorialism can both inform and be informed by work on Irish nation and state building.