European spatial planning arguments advocate a blend of strategic thinking, coordination and related initiatives to promote and secure territorial cohesion. These ambitions embrace a set of normative agendas around economic, social and environmental convergence, competitiveness, policy coordination and efficient infrastructure provision across space. In practice, territorial management then involves devising interventions across inter-connecting scales of governance which comprise complex agency relations, differentiated places and defined communities. In transnational contexts, attempts to foster appropriate spatial governance arrangements and relations across sovereign borders necessitate re-crafting planning and development cultures and service delivery practices to advance territorial cohesion. Transnational working necessarily involves cooperation across an extended range of institutions, interests, influences and potential actors. This paper examines attempts to secure bi-lateral commitment to a joint planning framework for the two distinct territories on the island of Ireland. Specifically, it traces the formal and informal activities involved in the development of the 2013 Framework for Cooperation between the Republic of Ireland and Northern Ireland. Informed by ideas of cross-border regionalism, it discusses the necessary spatial public diplomacy involved in the social reconstruction of strategic spatial planning to improve policy coordination and cross-border working.