European Union – Citizenship. Articles 18 and 21 of the Treaty on the Functioning of the European Union should be interpreted as meaning that, where an extradition request had been made by a third country for an EU citizen who had exercised his right to free movement, not for the purpose of prosecution, but for the purpose of enforcing a custodial sentence, the requested member state, whose national law prohibited the extradition of its own nationals out of the EU for the purpose of enforcing a sentence and made provision for the possibility that such a sentence pronounced abroad could be served on its territory, was required to ensure that that EU citizen, provided that he resided permanently in its territory, received the same treatment as that accorded to its own nationals in relation to extradition. The Court of Justice of the European Union so held in proceedings concerning an application for extradition made by the Russian authorities to the Finnish authorities concerning a Lithuanian and Russian national, for the purpose of enforcing a custodial sentence.