A German citizen who obtains another citizenship by application generally loses German citizenship, unless specific conditions apply or a retention permit (“Beibehaltungsgenehmigung”) has been obtained from the competent citizenship authority (BVA) prior to naturalisation.
As of 28 August 2007, a German citizen does not lose German citizenship by acquiring the citizenship of another EU member state or Switzerland. If this applies to you, you will not need a retention permit from the BVA and both citizenships can be kept.
If you applied for and obtained another citizenship (including EU member states and Switzerland) before 28 August 2007 without first obtaining a retention permit, you will in most cases automatically have lost German citizenship. In some cases you might be eligible for renaturalisation. More information: Renaturalisation and discretionary naturalisation
If you wish to apply for a retention permit, please submit your application to the Embassy in London or Consulate General in Edinburgh. Further information as well as the application form can be found on the website of the Federal Office of Administration (Bundesverwaltungsamt). In case you have any questions, contact us.