The Principality of Birkenfeld (German: Fürstentum Birkenfeld), known after 1919 as the Region of Birkenfeld (German: Landesteil Birkenfeld), was an exclave of the Grand Duchy and then the Free State of Oldenburg from 1817 until 1937, when it was incorporated into Prussia. It was located in the Nahe region on the left bank of the Rhine river and its capital was Birkenfeld. The government was led by a Government-President (Regierungspräsident) who was appointed by the government of Oldenburg.
The Grand Duchy of Oldenburg (German: Großherzogtum Oldenburg, also known as Holstein-Oldenburg) was a grand duchy within the German Confederation, North German Confederation and German Empire, that consisted of three widely separated territories: Oldenburg, Eutin and Birkenfeld. It ranked tenth among the German states, had one vote in the Bundesrat, and three members in the Reichstag. Its ruling family, the House of Oldenburg, also came to rule in Denmark, Norway, Sweden, Greece, Russia and United Kingdom.