Judgment of the Court (Grand Chamber) of 18 January 2022.#JY v Wiener Landesregierung.#Reference for a preliminary ruling – Citizenship of the Union – Articles 20 and 21 TFEU – Scope – Renunciation of the nationality of one Member State in order to obtain the nationality of another Member State in accordance with the assurance given by the latter to naturalise the person concerned – Revocation of that assurance on grounds of public policy or public security – Principle of proportionality – Statelessness.#Case C-118/20.