The Use of the National and State Flag
– The national flag is the German civil flag. It is also used as state flag by the non-federal authorities (e.g. the authorities of the German states use the German national flag together with their own state flag).

– The national flag is further used as state flag by the highest federal authorities (Bundestag, Bundesrat, Bundesversammlung, Chancellery, Constitutional Court) to show their connection to the German people. The other federal authorities use the Bundesdienstflagge as state flag. [...]