Résumé : The overall aim of this research is to provide a contribution to the current debates on EU actorness, in particular to its inter-regional dimension, by exploring the effectiveness of the EU in influencing regionalisation processes. As the process of regionalisation is the result of the interaction of different endogenous and exogenous drivers (Murray and Brennan 2015), this thesis focuses on the role of actors and goes beyond the conceptualization of the EU as a sui generis actor, by adding other relevant actors into the analysis, namely Australia, New Zealand, Japan and the US. It does so by applying an original analytical framework based on four analytical categories: the leader, the reference, the sponsor and the implementer and by exploring the role played by the EU within these four categories in comparison to other actors involved. By using a process-tracing methodology (Beach and Pedersen 2013) this research looks at the process of institutionalization of ASEAN regional disaster management. The empirical analysis of the institutionalization of ASEAN regional disaster management is divided into three parts: the first part is dedicated to the adoption in 2004 of the ASEAN Regional Programme on Disaster Management (ARPDM); the second part focused on the signature in 2005 of the ASEAN Agreement on Disaster Management and Emergency Response (AADMER); and the third part is devoted to the operationalization of the ASEAN Coordinating Centre for Humanitarian Assistance on disaster management (the AHA Centre). Despite the increasing emphasis within and outside the EU on the strategic importance of regional integration and inter-regionalism, this research shows how just sharing the label ‘regional organization’ and recognizing each other as a valuable partner is not enough to effectively collaborate together. Even more, this research advanced doubts on the effective role of the EU as ‘point of reference’ for other regional organization, demonstrating how –at least in the disaster management case- the initial reference role played by the EU was lost during the process. This research, while contributing to the theoretical debate on EU actorness, also has strong policy implications. First, it provides an updated overview of the disaster response policies implemented by the EU and ASEAN, thus contributing to the knowledge of both systems in responding to crisis. Second, the debate on the role of the EU outside its borders is on-going. The EU Global Strategy (2016) reinforced the importance of interregional organizations in EU external policies, yet too often the interregional bond is taken for granted and its concrete added value is lost in vague declarations.