The EU’s decision to grant Ukraine and Moldova a candidate country status and the recognition of Georgia’s European perspective in June 2022 has significant effects for both the EU’s enlargement and security and defence policies. So far, ‘hard’ security issues have played little role in the framing of the European Neighbourhood Policy (ENP) and the Association Agreements (AAs) with Ukraine, Moldova and Georgia. Their full integration into EU security and defence arrangements will thus require considerable strategy-making and implementation efforts. This article discusses the extent to which existing external Differentiated Integration (DI) constellations can be seen as ‘building blocks’ for Ukraine, Moldova and Georgia’s prospective full integration into the EU’s security and defence architecture. It is shown that, in legal and practical terms, such DI constellations are conducive to the deepening of these countries’ integration with the EU in the security and defence domain. From the political viewpoint, the focus on DI with the new accession countries may, however, be (mis)used as a substitute for fullscale integration into the EU security and defence architecture. We, nonetheless, suggest several pilot domains that can be used to test the limits of new accession countries’ DI with the Union.