The relationship between the nationality laws of the European Union Member States and European citizenship has long been the subject of academic discussion. The objective of the present paper is to investigate particularly the impact of the dual nationality regimes – for our purposes to be understood as the possession of a Member State and a non-Member State nationality – on access to European citizenship. Based on an analysis of dual nationality in three different historical-constitutional contexts (post-colonialism, post-emigration and post-communism), we argue that the use of dual nationality – in combination with a preferential nationality regime for certain groups residing outside the EU –, results in discrimination against migrants on the basis of their origin. The different dual nationality policies also affect the EU at large as Member State nationals enjoy – as European citizens – the right of free movement and residence in the Union’s territory. At the same time, however, it can be seriously queried whether these ‘external EU citizens’ can demonstrate a real link with the Member States granting their nationality. Finally, the examination of the case law of the European Court of Justice shows that tensions have already arisen between different Member State nationality laws; it is expected that these tensions will arise even more frequently in the future precisely as a result of the privileged route towards the acquisition of a second ‘European’ nationality. As the latter development is negatively perceived by many Member States, the EU may decide to undertake action in the area of nationality. This, in turn, could give rise to the legal autonomy of Union citizenship...