The European Union is often seen as a laboratory for a post-national polity. Leaving aside important discussions regarding exclusionary citizenship practices at the European level, this article draws attention to the on-going importance of member states’ citizenship traditions, which constrain the development of post-national citizenship in the EU. Considering the cases of Germany and the UK, the article shows how longer-standing citizenship traditions continue to play an important role in mediating relations between citizens and migrants. This, we suggest, remains the case despite changes to citizenship law over the past decades that have brought the two traditions closer to one another. Specifically, the article examines the on-going influence of each citizenship tradition with reference to political debates surrounding migration since 11 September 2001. It argues that divergent processes of ‘securitising’ migration reflect the respective citizenship traditions of the two member states.