Grand Duchy of Oldenburg in the context of "Union between Sweden and Norway"

The House of Oldenburg is a German dynasty whose members rule or have ruled in Denmark, Iceland, Greece, Norway, Russia, Sweden, the United Kingdom, Livonia, Schleswig, Holstein, and Oldenburg. The current kings of Norway and the United Kingdom are patrilineal descendants of the Glücksburg branch of this house.

The dynasty rose to prominence when Count Christian I of Oldenburg was elected King of Denmark in 1448, of Norway in 1450 and of Sweden in 1457. Denmark's current monarch, King Frederik X, belongs to the Glücksburg branch of the House of Oldenburg through his mother, Queen Margrethe II.

A grand duchy is a country or territory whose official head of state or ruler is a monarch bearing the title of grand duke or grand duchess.

Prior to the early 1800s, the only Grand duchy in Europe was located in what is now Italy: Tuscany (declared in 1569). During the 19th century there were as many as 14 grand duchies in Europe at once, some of which were revived after the Napoleonic Empire. Some of these were sovereign and nominally independent (Baden, Hesse and by Rhine, Mecklenburg-Schwerin, Mecklenburg-Strelitz, Oldenburg, Saxe-Weimar-Eisenach and Tuscany), some sovereign but held in personal union with larger realms by a monarch whose grand-dukedom was borne as a subsidiary title (Finland, Luxembourg, Transylvania), some of which were client states of a more powerful realm (Cleves and Berg), and some whose territorial boundaries were nominal and the position purely titular (Frankfurt).

Grand duke (feminine: grand duchess) is a European hereditary title, used either by certain monarchs or by members of certain monarchs' families. The title is used in some current and former independent monarchies in Europe, particularly:

• in present-day Luxembourg, the last surviving Grand Duchy
• historically by the sovereigns of former independent countries, such as Tuscany (from 1569 to 1860, now part of Italy)
• in Baden, Hesse, Oldenburg, Mecklenburg-Schwerin, Mecklenburg-Strelitz and Saxe-Weimar-Eisenach (officially simply the Grand Duchy of Saxony) – grand duchies from 1815 to 1918, and all now part of Germany
• formerly also in some countries in Northern Europe, such as the Grand Duchy of Finland or the Grand Duchy of Lithuania
• currently by claimants to the Russian Imperial Throne (eg. Grand Duke George Mikhailovich of Russia)

Oldenburg Land (German: Oldenburger Land) is a region and regional association in the German state of Lower Saxony in the area of the former Grand Duchy of Oldenburg (1815–1918), the later Free State of Oldenburg (1918–1946) and administrative district of Oldenburg (1946 to 1978), without its exclaves, along the rivers Hunte and Hase. In the region between coastline, Dümmer and Damme Hills some of the population still speak Low German today and, in Saterland also Saterland Frisian. The region is rich in old Lower Saxon customs such as Schützenfests or Kohlfahrten. Typical country sports include Klootschießen and Boßeln.

The mainly Catholic southern part of the Oldenburg Land is known as Oldenburg Münsterland, the mainly Lutheran northern part is known as Oldenburg Land (Old Oldenburg) in its narrower sense.

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 Regierungsbezirk Weser-Ems was the most westerly of the four administrative regions of Lower Saxony, Germany, bordering on the Dutch provinces of Groningen, Drenthe and Overijssel. It was established in 1978 by merging the former regions Osnabrück, Aurich, and Oldenburg. It was formally dissolved by the end of 2004 along with the other Regierungsbezirke of Lower Saxony as part of an effort to optimize the administrative system of the state.

The administrative centre of the Regierungsbezirk Weser-Ems was located in the Staatsministerium building in Oldenburg, a representative governmental complex from the period of the Grand Duchy and later Free State of Oldenburg. The department of educational affairs was based in Osnabrück, the department for financial affairs (Regierungskasse treasurer's office) in Aurich.