This paper explores how the European Court of Justice (ECJ) has implicitly amended the classical international rules on the recognition of nationality decisions among EU Member States. The major principles of international law on nationality state that 'any question as to whether a person possesses the nationality of a particular state shall be determined in accordance with the law of that state' (Art. 2 of the Hague Convention on Nationality of 1930). However, in the past 40 years the ECJ has delivered a number of judgments, where international rules on recognition of foreign nationality decisions were consistently disregarded, for example the principle of real and effective link (case of Zhu and Chen). Instead, the ECJ has developed its own, unique set of rules on the matter of recognition of nationality decisions, imposing stricter obligations on the Member States to recognise each other's nationality decisions and promoting the issue of gender equality in nationality law before it had a strong standing on the international level (cases of Airola and Van den Broeck). This paper analyses the case law of the ECJ and compares it to the established international principles. This brings up a number of questions, such as why the ECJ feels the need to diverge so drastically from the international principles. The answer might lie in the importance of the issue of recognition for the exercise of EU citizenship rights. Another interesting question is whether this justification for the ECJ to have diverged so radically from the international principles is sufficient, considering the lack of explicit competences of the EU in the field. Can this case law be seen as another example of judicial activism, infringing upon an area of exclusive competences of Member States? And if so, what are the implications of this shift of competences for the sovereignty of Member States in the questions of nationality, and for the relationship between the EU and its citizens?
