A German loses his citizenship with the voluntary acquisition of a foreign citizenship (Section 25 (1) sentence 1 Citizenship Act - StAG). In addition to an application for naturalization, the acquisition of a foreign nationality also includes acquisition on the basis of an option, by registration or declaration.

The loss of German citizenship does not occur if the German acquires the citizenship of another member state of the European Union, Switzerland or a state with which the Federal Republic of Germany has concluded a corresponding treaty under international law (Section 25 (1) sentence 2 StAG). In all other cases, the loss of German citizenship is avoided only if written permission to retain German citizenship has been granted prior to the acquisition of the foreign citizenship. Subsequent approval is not possible.

A retention permit may be granted if public or private interests justify the acquisition of the foreign citizenship and the continued existence of the German citizenship and no intergovernmental interests oppose the granting.

The decision in the retention procedure must be awaited before the other nationality is accepted or acquired. Otherwise, with the acquisition of the foreign citizenship, e.g. by naturalization, the German citizenship is automatically lost by operation of law.

The retention permit should be kept carefully, as it serves as proof of the continued existence of German citizenship despite the acquisition of another citizenship. Descendants who derive their German citizenship may also need to be able to prove this one day.