Judgment of the Court (Grand Chamber) of 17 December 2020.#Proceedings relating to the extradition of BY.#Reference for a preliminary ruling – Citizenship of the European Union – Articles 18 and 21 TFEU – Extradition of a Union citizen to a third State – Person acquiring Union citizenship after transferring the centre of his or her interests to the Member State from which extradition is requested – Scope of EU law – Prohibition on extradition applied solely to own nationals – Restriction on freedom of movement – Justification based on the prevention of impunity – Proportionality – Information to the Member State of which the requested person is a national – Obligation on the Member State from which extradition is requested and the Member State of origin to ask the third State requesting extradition to send the criminal investigation file