This paper looks at the relationship between the European Union and NATO and at how the two organisations cooperate on countering hybrid threats. Hybrid threats are multidimensional threats which include both conventional and unconventional tools and tactics (diplomatic, military, technological, economic) aiming to destabilise an adversary. During the last six years both NATO and the EU have established policies on countering hybrid threats and they have declared their willingness to start working together in this field. One of their key actions has been the creation of the ‘European Centre of Excellence for Countering Hybrid Threats’ in Helsinki. Therefore, the main puzzle that this paper aims to investigate is this: how do the two organisations cooperate on countering hybrid threats, given the problems associated with previous institutional arrangements (e.g., the Berlin Plus agreements)?