The article questions how strong Europeanisation is as an explanation of administrative changes in EU member states. Denmark has an opt-out from the European cooperation on defence, and, therefore, its defence administration represents a critical or a less likely case to test the Europeanisation thesis. The article shows that in spite of the opt-out, the administrative structures and the policy processes in the Ministry of Foreign Affairs (MFA) have adapted to the common foreign and security policy (CFSP) and the European security and defence policy (ESDP). Surprisingly, the administrative structures and the decision-making processes in the Ministry of Defence (MoD) have also adapted to the ESDP. The latter example emphasises the strength of top-down Europeanisation as a possible explanation of domestic administrative changes in member states. It is argued that Europeanisation per se is not an explanation of administrative adaptation. The pressure from Europeanisation has to be propagated by actors. In the case of the Danish defence administration, the promoter is government officials embedded in a domestic political-bureaucratic environment, which is remarkably positive towards the integration process within the EU. It explains the strategic choices of the officials, and, thereby, it explains the administrative adaptations of the MoD and the MFA.